Desantis lacks the big boisterous spray tanned clown face. The politics of trump (increased, you say, and I agree) would be brought back to the table without the big cartoon quality of trump.
The net effect of which would be a normalization of those specific politics. Desantis' public persona is far more normal than trumps is. No oompa loompa, no toddler tantrums, that sorta thing... You see? That's not a good thing, therefore it's better if trump stays on the ballot and the weak polls get addressed by something a little less senile on the Dem side.
Or continue to claim Biden is perfectly fine, and watch the swing states' differing opinion return the presidency to chaos, I guess.