The ball is in the court of the NFLPA when it comes to ratifying the new CBA proposal, which was approved by the owners  in February. The buzz is, they are secretly hoping the measure is rejected by the players, so they can redo the proposal with what they really want – an 18-game regular season schedule.
The current proposal includes a possible 17th regular season game beginning in 2021. The owner, feeling they slighted themselves in the deal, want it back so they can force an 18-game season on the players, who will be getting a bigger slice of the financial pie among other things.
From Jeremy Fowler of ESPN:
If the CBA is approved, the NFL regular season could not be expanded past 17 games through the life of the deal, which would run through the 2030 season.
But a handful of owners want an 18-game season eventually, the source said, and that could come up in future negotiations if the players don’t approve the CBA. A “no” vote from the players wouldn’t necessarily scrap the framework of the current proposal, but items would then be open for negotiation. A separate source told Fowler that if the owners pushed for an 18th game at that point, it might force the players off the negotiating table completely.
The players only need a majority vote of over 50% of the membership for the proposal to pass. The owners needed tree-quarters for the proposal to be approved. The players  have until 11:59 p.m. ET this Thursday and if passed, would be in effect for the 2020 league year.
According to Fowler some of the other issues the owners are backtracking on are:
 “The game-day roster increase from 46 to 48 players; the expansion of the practice squad to 14 players in 2022; and the lack of a proposed cap for the highest-paid players (essentially a quarterback salary cap).
\Minimum salaried players make up much of the NFL’s working body, and since those players will see significant salary increases under the new deal — second-year players rising from $495,000 to $675,000 next year, for example — there is some feeling that the new deal will pass. But some NFL locker rooms are divided because those in opposition feel the concessions aren’t enough to offset the lack of a 50-50 share or more long-term health benefits.”
As you can see, it’s all about health and money, as it should be. The players are at substantial risk (always have been) and with the league growing at an exponential rate economically, they want to ensure they are being protected and compensated accordingly.