Is there any interesting history behind this?
Yes.
When the
IETs▸ came in, the first one of the day was put on this route, really to provide a commuter service from Westbury and the Kennet Valley into London, and that service survives. The return service took the curve and avoided Westbury, again very much a Kennet Valley service and quiet by the time it got to Trowbridge.
That Westbury avoider had no regular passenger service prior to this train starting, and so it ran as an "experimental service" and was pulled a few days before it had been running for three years to avoid getting into a permanence that would make it somplex to close. The train now calls and Westbury and terminates at Frome, then runs back to Westburt and on, Empty, to Bristol.
To .... this is why I am careful to always say (well, not to the Amazon delivery man) that Trowbridge was no direct train service
from London.