People travel on the overnight coaches because they are very cheap. Good luck offering rail fares that match without insane levels of subsidy.
Those that fly would continue to do so because it's faster than either mode and doesn't involve travelling overnight in a seat.
What traffic congestion exists on motorways overnight even with closures for roadworks? Your have to divert or amend the rail service for overnight closures too, and good luck if you can't find a diversion that's practical....
Im also not sure where you get "noisy" from. Modern coaches are very, very quiet - probably less noisy than the creaking and squeaking of a MK4 gangway.
They're not very cheap - you're looking at £40pp per direction for an overnight coach end to end.
An all seated no frills overnight train wouldn't necessarily need huge amounts of subsidy.
Traffic congestion happens as a result of the coaches usually needing to leave a large city in the early evening (where there is congestion) to travel long distances.
And, while there are overnight railway closures of course, if you use routes that are kept open most nights for freight services that can be pathed around, the likelihood is significantly reduced.
Modern coaches are noisy not because of the coach itself, more because of the passengers on them. The background noise on an Mk3/Mk4 makes it more difficult to have a phone call at least!