Asking in context - isn't that a Sunday issue? On Monday to Friday - 21:04 off Paddington to Plymouth making all three of these calls, and also later travel to Westbury available with a Swindon change (21:31 off Paddington) and even later via Bath Spa.
Not sure what you mean by a Sunday issue. Are you thinking about there being less demand because it’s a Sunday?A few years ago, I’d have said yes. Now a lot more people travel on Sundays and later in the evening.
It stops at these stations Monday to Fridays, why not on Sundays?
To really answer that you would need to know how often that service runs on a Sunday's via the B&H▸ (Berks and Hants - railway line from Reading to Taunton via Westbury)