IMO, they only take that step in hopes of goading Trump supporters into violence.
From an electoral standpoint, DeSantis is almost as strong as Trump. If they can cheat and beat Trump, then they can probably cheat and beat Desantis as well, or alternatively, if they would struggle to beat Trump, they'd struggle with Desantis. Keeping Trump off the ballot might be satisfying to extreme leftists, but it wouldn't do a lot to further their mission.
One thing for certain, there's always more going on than meets the eye. If they were that concerned about Trump himself, they'd just heart-attack gun him.