The US late night shows are interesting. They tend to leave in mistakes or sketches bombing because there isn't enough time to do something else before transmission. Though of course the reaction to the sketch falling flat might be deemed funnier than the actual sketch itself.
For example, here's a Johnny Carson bit
that bombed one night. The sketch is abandoned part way through with all of the reaction afterwards included. However, in the description, it's revealed that the same sketch was done again the very next night, with no introduction or anything, and was a success.
I've personally never liked most of the late night shows except for Conan. I find quite a lot of his comedy bits funny, but I wouldn't be bothered to watch a full edition with the traditional monologue or celebrity interview (which even he has tired of now, cutting his show down to half an hour with commercials).
I can also appreciate some of the more surreal and inventive work David Letterman did in the '80s on his NBC Late Night show, which is getting slowly uploaded bit by bit to this amazing YouTube channel: https://www.youtube.com/user/dongiller
I think it's just a different culture to ours where the late night format has become part of the TV landscape. And remember, James Corden's show goes out at 12.35am, which seems incredible to us, given a show like that here probably wouldn't start any later than 10.30pm.
The 2019 ratings for the US talk shows have plummeted but are still popular, especially with their online content. Compared to the hey day of Johnny Carson, Jay Leno and David Letterman, the overnight ratings are pittance, but overnight audience are not really the profit makers for advertisers now.
For example: In early May 2019, the average overnight ratings for The Tonight Show starring Jimmy Fallon was 2.4 million, The Late Show with Stephen Colbert was 3.8 million, Jimmy Kimmel Live was 2 million, Late Night with Seth Meyers was 1.4 million, Late Late Show with James Corden was 1.3 million, Daily Show with Trevor Noah was 650,000 and Conan was 340,000.
Real Time with Bill Maher averaged 1.6 million on HBO (full subscription channel). Last Week Tonight with John Oliver averaged 1 million. Samantha Bee's Full Frontal averaged 900,000.