Here's a pretty pointless feature from The Guardian asking why Seinfeld wasn't a hit in the UK. Simply because the BBC could not give one fuck about it. Once I sat up to watch an episode, scheduled for around midnight, and I'm not making this up by the way, this did happen, only to discover that it had been cancelled to make way for shinty. That's no wacky random thing I've came up with, it was genuinely cancelled in order that BBC show highlights of a shinty match that had by the looks of it only about 30 spectators at the actual game.
I once bought an unofficial guide to Seinfeld. As you'll see by the photo in the link it's endorsed by the BBC. That about says it all on their commitment to the show.
You could ask why a lot of US sitcoms weren't hits over here and it's all pretty much down to scheduling. In the link on top US sitcoms that I featured yesterday Night Court is included. It also appears on one of the links in that article at 18th in the list of most watched TV show finales. Why was Night Court not a hit here? It wasn't because we didn't enjoy Harry Anderson and John Larroquette's clowning, it was cos it appeared infrequently late night on BBC2 (if I mind right).
A good and popular sitcom in the US has no guarantee it's going to be a success here and that's usually because whoever imports programmes and schedules them for the terrestrial channels over here has to be convinced first. Let's not even get started on Arrested Development.