As a regular commuter (and newbie on here) between WSM and Temple Meads I know too well the problems about "last" trains home
As we stand the below are the last trains on each of these evenings from Temple Meads back to WSM:
MONDAY 23:36
TUESDAY 23:36
WEDNESDAY 23:36
THURSDAY 23:36
FRIDAY 23:36
SATURDAY 22:17
SUNDAY 23:12
I've always been amazed that there is a later service on a Sunday evening rather than a Saturday
When a service is specified as part of a franchise or management contract, one of the elements specified usually relates to the times of the first and last train. For example "The first train will arrive into Thamesdown Central no later than 08:30 and the last train will leave no earlier than 17:30".
The issues of first and last trains are very much on the radar for the next Great(er) Western franchise. The team putting together a draft specification on which to have a public discussion / consultation next year have sought inputs as to where passengers would like to see first and last train updates ... far from cast in stone, of course, but a sensible idea of where to start the fine tuning from.
Bristol to Weston-super-mare isn't the only service to finish earlier on a Saturday, by the way - Westbury to Swindon is another, with a last train at about 18:30 on Saturday and after 19:30 the rest on the week. Sunday evenings can be very busy with longer distance traffic, so the later services that night aren't a surprise even if buses - typically shorter distance - are thinnest on a Sunday evening.