In Liverpool there's only one night bus and it literally goes from one end of the Birkenhead Tunnel to the other, on the hour
They did experiment with night buses but gave up when the police got called to many services, one route even had a police car follow every service
That might give some sort of clue as to why they don't exist.
WIth regards to trains, they tend not to happen because a lot of minor maintenance and checks are done in the 5 hour window of no trains