Giants first baseman Brandon Belt could have been a free agent for the first time this winter. Shortstop Brandon Crawford, too. They’ve each compiled six full seasons of service time, earning the right to test their value on the open market.

Good thing for both that they signed extensions.

“I’m very thankful I am where I am right now and don’t have to deal with all that,” Belt said.

Had Belt and Crawford been free agents, they might be among the players gathering Tuesday in Bradenton, Fla., for a union-sponsored training camp for free agents.

As the Giants’ players gathered over the weekend for FanFest, many expressed concern in Chronicle interviews that the game is being hurt by a slow free-agent market and teams’ unwillingness to compete, which has created labor strife.

“It’s definitely troubling as a player to see that many good big-league players still unsigned,” Crawford said. “Those are guys who can make huge impacts on teams, and teams are not going the extra year or extra million dollars or whatever to sign those guys. That’s definitely troubling.”

Belt said fewer suitors “take away from the competition, and competition is good for everybody. It’s worrisome.”

Over the weekend, pitcher Yu Darvish got a six-year, $126 million deal from the Cubs, but more than 100 free agents remain unsigned, including pitchers Jake Arrieta, Alex Cobb, Lance Lynn and Greg Holland and hitters J.D. Martinez, Eric Hosmer, Mike Moustakas and Jonathan Lucroy.

Several top free agents are clients of agent Scott Boras, who has training facilities in Florida and Arizona. The union arranged a camp for the first time since free agents sought jobs at the end of the 1994-95 strike. It’ll be overseen by former Houston manager Bo Porter, an A’s outfielder in 2000.

“When you look at a guy like J.D. Martinez, in a normal offseason, it feels like at least a dozen teams would go out to sign this guy,” Crawford said, “and this year, I heard of only two, the Diamondbacks and Red Sox. That part, to me, doesn’t make sense. This guy can be a team-changing offensive bat.”

The Giants had some degree of interest in Martinez before acquiring outfielders Andrew McCutchen (from Pittsburgh in a trade) and Austin Jackson (for two years and $6 million). They also traded for third baseman Evan Longoria in a bid to upgrade an ineffective lineup.

Though agents have alleged collusion among owners, traditionally high-payroll teams (including the Giants) are determined to stay under the $197 million competitive-balance tax threshold to avoid penalties.

Some teams’ payrolls will fall just short of the threshold and other teams won’t come close. A third of the teams would say they’re rebuilding, though the union and agents would call it tanking. According to union chief Tony Clark, it’s a “race to the bottom.”

“The only thing that I see, that stands out to me,” pitcher Madison Bumgarner said, “is there are a lot of teams that are not willing to compete in 2018.

“There are a lot that are. But there’s definitely a good bit that are not.”

Bumgarner’s $12 million option was exercised by the Giants, keeping him off the free-agent market. He has another team-friendly option for 2019.

“I’ve got to worry about what I can control, and that’s it,” Bumgarner said, “but as a fan, that’s not really fair to the game and to the cities. You would like to be able to start every year and ideally not have a favorite to win that year; everybody gets a chance. It definitely doesn’t seem that way.

“We might be proven wrong. One of these teams might win. That’s why we’ve got to play the season. But on paper, it certainly seems that way. I just see a long list of (free agents) who are still out there.”

Giants executive vice president Brian Sabean wouldn’t compare current friction to 1994-95 — “There’s a (labor) deal in place,” he said — but couldn’t explain the stalled free-agent market.

“I don’t know if it’s a one-year correction,” he said. “I don’t know that anybody in the game is smart enough to know what it means.”

The only free agent the Giants signed to a multiyear deal was Jackson, who was a free agent for the third straight winter and signed Jan. 22. In 2016, he didn’t sign with the White Sox until March 6, with spring training already under way.

“It’s unfortunate,” Jackson said of his unsigned colleagues. “You can sit there and wonder, ‘Am I going to get signed? Am I even going to play this year?’ I’ve been through that. It’s tough on you and your family, and it can take a toll on you.

“Hopefully, those guys can get something done because there are a lot of good ballplayers out there that need to be playing.”

McCutchen can be a free agent after next season, along with Bryce Harper and Manny Machado, a class that’s anticipated to be among the best in history. It could get deeper if a few of the top current free agents accept one-year deals.

People in the industry wonder whether next year’s class will run into similar roadblocks.

“The people want to see the players,” McCutchen said. “That’s what they come to the ballparks for, to see the guys who make the game exciting. That’s what it’s all about. Fans don’t want Machado or Harper or (Clayton) Kershaw, if he opts out, not to be in uniform. It’s all about the fans, man. That’s why they come out, why they get TV packages, to see the players.”

Matt Cain was the Giants’ longtime player rep (liaison between the union and teammates) before retiring, and the duty falls to reliever Cory Gearrin this year. The assistants are Crawford and Buster Posey.

“I get teams want to have no luxury-tax penalty for whatever consecutive years because penalties are tough,” Crawford said, “but there are other teams that are far under the luxury tax, and they could easily pick up some of these guys.

“It makes it look like they’re not trying to win by getting the best players. If you’re trying to draw more fans, and you want to expand the game, you should have the best players playing. I don’t think this is good for baseball.”

John Shea is The San Francisco Chronicle’s national baseball writer. Email: jshea@sfchronicle.com Twitter: @JohnSheaHey