There are few rovers valid in the SWT area, so can't imagine SWT guards issue them very often.
Heart of Wessex Day Ranger
Freedom of Severn and Solent
Freedom of South West
Freedom of Devon and Cornwall
Devon Day Ranger
Devon Evening Ranger
All Line Rover
North Downs Day Ranger
Thames Rover
Freedom Travelpass
I don't think 10 products valid on SWT services can be described as few.
Not knowing how to use TIS to their full potential is however endemic across the rail industry, not just limited to on train sales. Just yesterday I had a ticket office tell me there was no such thing as a Heart of Wessex Day Ranger.
I also can think of no logical reason why some TOCs tell their on train ticket sellers not to sell certain products despite that product being available for use from a passenger's origin station.
And don't get me started on that stupid Condition of Carriage rule that says if the ticket type you require is not available from origin station TVM you must buy a ticket to cover part of your journey. I did this once when I wanted a Rover and the conductor refused point blank to accept the ticket in part payment and I waited over a month for the TOC to refund the original unnecessary ticket.