You don't think the players lose negotiating power by agreeing early? Isn't their only power the threat of missed games?
Say you are a minimum salary player. You make $585K per season, give or take. That is, if you make the roster. Pretty easy to cut minimum salary players, after all.
This deal expands the roster by 2 positions. Good for you, since it makes it more likely you stay on the roster each season.
This deal would mean an extra ~$500K for you over the next 3 seasons. That is a raise of 25%+ for you.
This deal also improves your benefits. Something more valuable to the lower salary players.
This deal also reduces offseason requirements. Not a critical issue, but positive.
This deal also allows you to use MJ without potentially serious punishment from the league, if that matters to you. A possible positive.
Meanwhile, all of this starts in 2020 if you vote yes. If you vote no, the ultimate new deal might not begin for another year. You might not even still be in the league.
Now. Tell me how you vote.