The man was scared to debate RFK Jr. You think he's ready to go one-on-one with Haley, Vivek, and other bright minds
Doing all these debates requires a ton of preparation. You have to read a lot; you have to do mock debates. He probably doesn't have time to do 5 random one-on-one debates (in addition to the 3-4 debates he'd do against Trump in the general)
He wasn't scared, there's just no need to debate someone as an incumbent when you're this far ahead. RFK was scared to directly run against Biden which is why he left the primaries and tries to get his 1% as indie candidate (if his "campaign" even makes it to November 2024, which I put a question mark on).