It may be to do with rostering of staff, less disruptive to roster patterns to keep to the standard timetable
As one reason, that would make sense. I also note that bank holidays are now very much more a part of the working week - no longer are they "everyone stops" but much carries on as normal with days taken off in place. Our dustbins were collected yesterday (or, rather, their content was!) on the normal cycle, Melksham Campus remained ope =n where it used to close on bank holidays, etc. So there is a much-grown requirement for people to get to work on these 8 days in the year as well as the leisure traffic. So perhaps whilst a few extra fill in trains could be lost (such as that 05:11 south of Salisbury), those former
BHX▸ service are now vital on those days where they formally did not run - even if lightly loaded, they are now vital trains where there is no close alternative such as the 05:11 north of Salisbury.