Trump doesn’t adapt his strategies with new information. At the beginning of the campaign, DeSantis looked like a credible opponent, so Trump is still behaving like he is. Look at 2017 when Trump was loudly complaining about voter fraud in an election that he’d won. He’d already decided that he was going to spend his time after the election complaining about voter fraud, and he stuck to that despite the fact that it made no sense after his victory.