Kelvin Kuo/Associated Press

Never have so many NFL stars seemed so unhappy.

At least, that's the belief among some NFL teams, who claim they've never seen so many prominent players involved in contract disputes.

In Pittsburgh, there's running back Le'Veon Bell, who could hold out well into training camp. Falcons receiver Julio Jones skipped a mandatory minicamp, and I've been told by numerous sources that he wants to be the highest-paid receiver in football.

In L.A., Rams defensive tackle Aaron Donald skipped OTAs and this week's mandatory minicamp. Seahawks safety Earl Thomas and Arizona running back David Johnson also were missing this week as they both pressed for new contracts. And though Giants star Odell Beckham Jr. did show up for camp this week, he likewise wants a new deal.

Finally, there's Aaron Rodgers. The star Packers quarterback appears headed for a contract extension before the season, but not without having voiced some concerns in the offseason over the direction of the organization.

Those seven players have a combined 28 Pro Bowls between them.

We've seen stars have contract disputes before. We've seen them want more money. What we've never seen is this many big names simultaneously wanting new deals.

"It's as if there's a desperation across the league," one high-profile agent wrote to Bleacher Report. "Players know the union sucks and are worried about the new CBA. Plus, coincidentally, a lot of really good guys have outplayed their deals."

While I differ on the agent's view of the union, a lot of players around the league do not. As such, they are growing increasingly more assertive in advocating for deals they feel are more in line with what they believe to be their true value.

As one Pro Bowl player told me, players are becoming more aware not only of their individual worth, but the fattening of the owners' wallets as well. And they're getting no help from a collective bargaining agreement many feel is outdated and doesn't account for the skyrocketing money owners are earning from the increasing values of their teams.

Phelan M. Ebenhack/Associated Press

It isn't that players want to be paid more than the next guy at their position. It's that they want to be paid more than the next guy because that guy is getting his, and I need to get mine.

Good for them. They deserve every penny they get.

But we all better get used to this new reality, players and agents say. Missed minicamps and holdouts through training camp will become more frequent. It will be unusual for a player halfway through his deal not to want a new contract.

Why? It's simple: The money keeps growing.

Hell, who can blame them?

Consider Jones. He watched as his teammate, Matt Ryan, signed a five-year contract extension worth $150 million last month. If you're Jones, you're probably ecstatic to see your teammate make tons of cash. Cool, bro. Do you. Let's go for drinks later.

But, hey, what about me?

It may be the same scenario Bell faces in Pittsburgh. Teammate Antonio Brown signed a contract in February 2017 that made him the highest-paid receiver in football at $17 million per season.

As Sports Illustrated's Jonathan Jones noted, Jones is making an average of $11.475 million throughout the rest of his deal. That's almost $6 million less than Brown annually.

Brown is good, but he isn't $6-million-over-Jones good.

Jones, though, has a staggering three years left on his deal. If the Falcons redid his contract (and they will), it likely would be unprecedented in the history of the team.

Adam Hunger/Associated Press/Associated Press

Another motivating force behind the rash of contract squabbles in the NFL are the megadeals that have been handed out in the NBA in recent years.

Many NFL players and NBA players are close, and NFL players see the kind of money NBA players are making. Not the stars like Steph Curry, but mid-level players making tens of millions of dollars to be sixth and seventh men on rosters.

This does not go unnoticed by NFL players.

Last July, Bills receiver Sammy Watkins tweeted: "We gotta get paid more." He noted the NFL is the most-watched sport in the U.S., but NBA players "make way more."

When the NBA's salary cap jumped an unprecedented $24 million in 2016, Jeff Diamond of Sporting News recapped the reactions from NFL players.

Broncos receiver Emmanuel Sanders tweeted, "Looks like I chose the wrong sport."

Safety T.J. Ward said, "We getting peanuts compared to these NBA and MLB cats! Whoa."

Colts punter Pat McAfee tweeted: "Hey NFLPA. Let's chat with the folks from NBAPA ASAP."

None of this will change soon. The contract fights will continue. The holdouts will continue.

The battle for what makes the NFL run—cash—continues.

Mike Freeman covers the NFL for Bleacher Report. Follow him on Twitter:@mikefreemanNFL.