(CNN) The most diverse field of Democratic presidential candidates in history is now boiled down to a debate stage that lacks black or Latino candidates .

The Democratic National Committee on Friday unveiled the list of seven candidates who met the polling and fundraising minimums to qualify for the December 19 debate in Los Angeles. It includes one person of color: entrepreneur Andrew Yang

The announcement comes amid a labor dispute that has threatened to derail planning for the debate at Loyola Marymount University. The food workers' union has said it plans to picket the debate, and all seven candidates invited to participate said Friday they will not cross the picket line. The DNC said Friday afternoon it is "working with all stakeholders to find an acceptable resolution" that allows the debate to go on without expecting candidates to break with the union.

New Jersey Sen. Cory Booker will miss the stage for the first time, and former Housing and Urban Development Secretary Julián Castro is off-stage for the second time. California Sen. Kamala Harris dropped out of the race, and a late entrant, former Massachusetts Gov. Deval Patrick, hasn't yet come close to qualifying for a debate.

The trimmed-down debate lineup has frustrated some Democratic donors, operatives and activists who hoped to see a field more representative of the party's base. It also underscores a reality of the 2020 race: Polls and fundraising numbers reflect that candidates of color just aren't getting much support from voters of color.

"The dominance of white candidates in the race confirms something we should have already known: The political system was not set up to include candidates of color," Democratic strategist Jess Morales Rocketto said.

"As the Democratic Party begins to align its leaders with its base, the party apparatus needs to address the systemic barriers that still exist for non-white candidates," she continued. "It's not on the party to solve racism or sexism, but it is on them to make sure they address systemic barriers for non-white candidates."

The smaller debate stage might reflect the favorites of established Democratic voters and donors, but makes it harder to expand the party's electorate, some organizers said.

"It is particularly disheartening to see that the folks we organize won't be able to watch the debate and see anyone who looks like them," said Quentin Savwoir, the political director of Make It Work Nevada, an advocacy group that organizes women of color. "Cory Booker's story, Kamala Harris's story -- that resonates differently with the folks we work alongside, because they understand what it means to have lived those experiences."

He said he didn't want to diminish the presence of Yang on stage, since Asian American and Pacific Islanders are the fastest-growing demographic in Nevada, but called it disappointing that the Democratic Party is "still not investing in people of color as candidates."

Others point out that the winnowing stage is the reality of a field where non-white candidates have failed to galvanize non-white voters. Former Vice President Joe Biden has dominated in polls among African-American voters, and Biden and Vermont Sen. Bernie Sanders have shown the most strength with Latinos.

"What voters are saying is, you don't have to look like me to represent my interests," said Antjuan Seawright, a South Carolina Democratic strategist. "Like it or not, say what you want about that, that's the reality -- that's what the voters are saying. That's not the party. That's not the election being rigged. That's what the voters are saying."

"You have to play with the hand that you're dealt," Seawright said. "Some people will always attack what's not working for them."

Biden, Sanders strongest among non-white voters

The candidates who qualified for this month's debate are Biden, Yang, South Bend, Indiana, Mayor Pete Buttigieg, Minnesota Sen. Amy Klobuchar, Vermont Sen. Bernie Sanders, investor Tom Steyer and Massachusetts Sen. Elizabeth Warren.

Biden last week told reporters that the debate stage is "not representative of the Democratic Party."

"But you can't dictate who is going to be the nominee, who's going to be able to garner votes, who's going to be able to stay in the race," he said.

He pointed to Harris' abrupt exit from the race, saying she is "a really talented person" but that the decision to drop out was hers.

"She was capable of being anything from president to vice president to secretary, to be a Supreme Court justice, to be an attorney general. I mean, but, you know, who controls that except the candidates themselves?" Biden said.

Booker and, until she dropped out, Harris, have often talked about re-engaging the "Obama coalition" -- a group of voters that included those who are young, non-white and college-educated women -- as crucial to the Democratic path to victory in 2020.

However, polls have shown that non-white voters are sending the message that representation isn't all they are looking for in a presidential nominee.

Biden has dominated among black voters, particularly in South Carolina, where polls have consistently shown him with 40% or more support overall -- and even larger support among African Americans. They're a crucial portion of the Democratic electorate, particularly in Southern states where Biden can rack up delegates.

The consistent support for Obama's former vice president among black voters has all but closed down the paths to the nomination for Booker, Harris and Patrick. It has also put a hard ceiling on Buttigieg -- who has surged in Iowa and New Hampshire, but struggled to answer questions about where he can win after those two largely white states.

Sanders, meanwhile, has surged with Latino voters who are crucial in Nevada, the third state to vote, as well as Texas and California, which both vote on Super Tuesday on March 3. He has benefited from an endorsement from New York Rep. Alexandria Ocasio-Cortez and being branded "Tío Bernie," and used his closing statement in November's debate to reach out to immigrants and their families.

Candidate complaints

Castro and Booker have both talked in recent days about the diversity of the Democratic 2020 field -- and

Castro has been by far the most outspoken candidate to criticize the Democratic nominating process.

He said last week in Iowa that he isn't asking the DNC to change its debate rules in the middle of the election cycle. But he said going forward, Democrats need to "change the game" and do "something much more meaningful and deeper than that."

"When they don't reflect the diversity of our party or of our country, and that if we truly value black women, for instance, and we keep telling them that they're the key to our success in places like Louisiana and Alabama, and that they're going to be key in 2020, then, why do we start the most important nominating process in our whole party, the presidential nominating process in two states that hardly have any black people in them?" he said.

Castro's comments have appeared to be a play for future presidential races -- and comes after he's laid off some campaign staffers and others have left for other jobs.

Booker, meanwhile, is insisting he still has a path to the 2020 Democratic nomination.

"I may not be on the debate stage next Thursday, but thanks to the outpouring of support from this community over the past few weeks, we know there's a path to victory and we no longer need the December debate stage to get there," he wrote to supporters in an email this week.