Jerry Seinfeld phrased it out most concisely when he said, " The talk all around the comedy bars was who was going to take over 'The Tonight Show' after Johnny Carson. Never did anyone expect he would pack the show and take it with him". Jerry has a massive sitcom to boast about, but he never could be a 'Tonight Show host. So let's look into what happened to Tonight's show.
Johnny Carson was the best comic of his age and only natural that he would take over the Tonight show, America's biggest talk show. With his calibre, he put the show to its prime. David Letterman, a young, engaging host, was given a new 'Late Show' to train under Carson's guidance. However, one ambitious comic, Jay Leno, had eyes on that coveted seat. So in 1991, Leno's manager planted a story in the media on how NBC was planning to replace Carson with Leno. This came as a shock and humiliation to Carson, who quit the show hastily.Meanwhile, NBC wanted to avoid parting with the money-making letterman show. Thus the arrangement came as Leno took over Tonight Show and Letterman in his status quo. Carson and Letterman were devastated by the progress of so many comics. Letterman didn't want a Late Show anymore and thus switched to CBS and a new theatre.
If you thought the tonight story was over. There is still some drama left. Upon Letterman's exit, NBC found a new face Conan O'Brien to take over the Late Show. It was a young man fighting for space in a late show while Leno and Letterman had their battle for prime time. Conan fought this lost game for a while until he found everything collapsing. In 1994, when the late show was to be cancelled, something unique happened; Letterman appeared in his ex-show, perhaps saving Conan from an imminent cancellation. By then, Letterman, the top host and his popular support gave drowning Conan a straw. And Conan did catch it very well, rising in popularity, so much so that in 2009 he was planning to take over Leno. Old comics were worried that Leno was shrewd enough to let a show go.
In 2009, Conan was given the Tonight Show, only to find in five months that Leno had taken over the time slot before him. Essentially guests were handed over to Conan after Leno had used them. Thus his ratings fell, giving Leno a narrative to get back the Tonight Show. Midst public outcry, Leno took over the show, as Conan moved to TBS. Conan and Letterman did have an episode together on how Leno had successfully demolished a generation of good hosts from entering the Tonight show, just by politics and NBC's apparent blind eye to it. Letterman's show was handed to Stephen Colbert, who still leads the ratings.
In 2014, Leno finally quit the show. Jimmy Kimmel was the best man to take over, but he didn't dare engage with Leno, who wouldn't want the next host to be better than him. Finally, NBC found Jimmy Fallon for the Tonight show and Seth Meyers for the late show. Meanwhile, Conan has quit his role, using his popularity to move to a streaming channel. But NBC is still a household name and would enjoy that advantage. But indeed did; it probably lost 4 best hosts just to accommodate Leno.