I think the primary difference is Andy Richter's apparent enthusiasm - one might infer, from the latter clips, a "the other shoe finally dropped" feeling.
shortly after Conan got the tonight show, NBC had a "boy we made a mistake" moment (or realized Fallon would be a better long term choice) so purposely shuffled Leno back in for a bit, BEFORE THEN giving it to Fallon so that Fallon wouldn't look like 'the guy that stole the show from Conan' -- just think about that before brushing it off
Not at all. Conan is a far better late night talk show host than Fallon ever was, and it was Jay Leno’s doing. If he truly wanted to let go of the Tonight Show he would’ve signed on with another network instead of trying to muddy things up in the time slots.
Nah, what happened was that NBC didn't want to lose Leno to ABC or FOX or something, so they gave him that 10PM nightly slot. But that fell through in ratings. While that happened, because Leno STILL got the bigger guests because he was on first, Conan's show suffered because he couldn't get those guests (just think of if CONAN got that interview with Kanye West right after his "Imma Let You Finish" stunt he pulled: Conan would STILL be hosting The Tonight Show right now, I bet), even though his show was doing okay despite it being, GASP, eclipsed by David Letterman, which it had never been since the Hugh Grant interview in 1994 IIRC. NBC cancelled Leno's disaster, and was going to give him a 11:30 half hour show and bump Tonight Show. Conan refused, saying that it would damage the tradition of that show. They instead gave Leno the slot back and bumped Conan out. Had nothing to do with Fallon. He was in the right place at the right time, since he was just sitting there doing Late Night and making his own mark and showing he could do things well. Conan and Fallon both proved themselves. It's just how NBC mismanaged everything by not wanting to move on from Leno.
Conan is more of a cult favorite. He has a relatively small base of extremely devoted fans, including me. That was enough to get him good performance on "Late Night," but I imagine he was off-putting for much of the broader 11:35 audience, who had already seen Leno at 10:00. But not many people were watching Leno at 10:00, and that killed ratings for the 11:00 local news and then for Conan. Conan went up against Letterman, but Leno was up against "CSI: Miami." Jimmy Fallon has broader appeal like Leno did. It doesn't mean Fallon is better. It just means Conan is an acquired taste. But once you "get" Conan, you realize how brilliant he is.
ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-_z57cfafysI.html this comment is 4 years old but this gives a pretty damn good insight into what happened and why leno is so hated