Something strange is happening with the baseball hot stove this winter. Not only is it not hot, it almost seems like it’s off.

Available stars who would ordinarily have been snapped up long ago are still sitting on the shelf, which has the MLB Players Association panicking — and looking for answers. Is this simply a weak class of free agents? Have all 30 teams finally figured out that spending boatloads on veterans is usually dumb? Is the gap between contending and tanking teams to blame? Or is it just — gasp! — collusion, like the kind owners engaged in three decades ago?

It’s difficult to pin down exactly why this offseason has proceeded so slowly. But the sluggish pace it has taken is quantifiable — and eye-catching. I gathered data on ESPN’s top 40 free agents for each winter going back to the 2006-07 offseason and tracked how many days it took after the end of World Series before those top players were signed. (Players technically become free agents the morning after the World Series ends.) For instance, today is Day 82 since the Astros beat the Dodgers in Game 7 of the Fall Classic, and only 43 percent of the top 40 free agents — including only two of the top 10 — have put pen to paper. How abnormal is that? Between 2006 and 2016, the average offseason saw 76 percent of the top 40 free agents inking deals by Day 82 of the offseason.

Here’s what this offseason looks like so far compared to how long it usually takes for top free agents to sign:

The freeze on this year’s class of free agents is alarming. For one thing, it took much longer than usual for a team to break the free-agent ice. And, aside from a brief acceleration during the winter meetings in mid-December, the pace of signings has been markedly slower than normal — particularly early in the offseason, when the biggest flurry of signings usually takes place.

Only the 2008-09 offseason, when just 53 percent of top-40 players were signed by this stage of the winter, came close to lagging as much as the current slowdown. And even then, most of the biggest available names had already been signed by this point in the offseason. Granted, three of those (Mark Teixeira, CC Sabathia and A.J. Burnett) were all picked up by spendthrift Yankees. By contrast, the current Yankees made their big splash in the trade market, where they acquired Giancarlo Stanton, and the team is now trying to squeak in under the luxury-tax threshold rather than adding free agents. Perhaps in the past, slow free-agent classes could always count on the Yankees to open the pocketbook and keep the money flowing — but not this year.

Before we jump to any conclusions about the owners being in cahoots, it’s worth noting that many of the explanations for this year’s issues contain at least a kernel of truth. This class of free agents is indeed mediocre — in terms of wins above replacement produced by top-40 players in their previous three seasons, this is the worst crop of available talent since at least 2006. At the top of ESPN’s free-agent rankings, ace starter Yu Darvish is as good as any prized free agent from yesteryear, but many of the names further down the list come with legitimate issues, including Jake Arrieta’s declining value, J.D. Martinez’s inconsistent defense and Alex Cobb’s durability.

It’s also true that more teams are tanking now than in years past. And the proliferation of statheads in MLB front offices over the past decade could explain why teams are no longer scrambling to offer big free-agent contracts to players who are already past their primes.

As Yahoo’s Jeff Passan wrote in an excellent column last week, that final point is part of a bigger issue with the fundamental way baseball’s economics works, particularly as younger players generate more and more of the game’s on-field value. But if teams are suddenly realizing the folly of free agency, it’s also worth asking why they’ve chosen to simultaneously make their stand this year. (Bad deals still got made last season, though perhaps not as many as in the past.) The alternative explanation — collusion — is notoriously difficult to prove, however, and seems like an unbelievable risk for a group of owners who are already making money hand over fist.

But the simple truth is that we don’t really know why the market for free agents is so sluggish this year. We can only prove that it is indeed historically slow-moving — and that fact alone demands an explanation.