1. There will be no undecided voters, they are all for Biden.
2. There will only be gotcha questions.
3. NBC will make a ton of money because the ratings will be huge compared to Biden's townhall.
Trump wanted to debate. It is unfair to debate a senile old man who requires a teleprompter and a wire, and drugs just to stay coherent, so Trump instead decided to debate the moderator with Biden in absentia.