I'm on record earlier as saying these "debates" are worthless as a pile of crap. Less so, because at least the pile might become fertilizer.
Or, they should be looked at that way. It's like me holding a sack race around the conference table in order to pick a new programmer. Entertaining, tells me nothing about how the winner might do the actual job. I've never held an interview with a candidate where the opposition is there flinging insults and interrupting. But anyway.
But Joe has to agree to "debate", because if he doesn't it will be held against him by the moronic public who might actually use these jokes to pick their horse. Or people who don't actually have even the tiny bit of attention span to watch even these, but who would see headlines that Biden is too scared/too old/too full of Alzheimers to attend. I find that ludicrous, but that's the public for you.