The 2AM stuff is the less valued programming by the network to be sure. There are a lot of people in the US with varying work schedules, so it's completely up in the air in terms of who's watching. At least if you're not the folks at Neilson.

The most valuable post-prime time "talk show" window is 11:30pm to 12:30am. These programs are on after the local news which goes from 11-11:30 or 11:35.

Viewership is probably pretty high but obviously not as high as during the 8pm-11pm prime time block. That's why the programs are talk shows which are comparatively cheap to produce versus sitcoms and 1-hour scripted shows. They're filmed in the afternoons, so the hosts, guests and live-audiences don't actually need to stay up.

This whole cock-up is because NBC have been managed by sub-human cretins for years who obviously don't know much about selecting, showing and keeping ratings-winning programming.