It's not really a liability though, is it?
Technically either company could withdraw the scheme at any time.
It doesn't cost them anything
Free tickets might cost companies money, if people use them for journeys they would otherwise pay for.
Also they have to make sure staff know how to deal with the passes, and get it right enough not to jeopardise goodwill.
I think it sends a poor message that the first thing ticketing wise the new franchisee does is to withdraw something from people who pay high fares (and subsidise the rest of the railway as a result). Now THAT is poor business practice.
Maybe people's expectations vary a lot when franchises change. Perhaps as with other aspects of the railway, people have different ideas about how much decisions are, or should be, under government control as a public service.
SWR decided not to continue the scheme for new season tickets, particularly affecting people whose ticket was going to run out soon - apparently without warning.
They wrongly said this was in the original terms.
Conceivably, someone who has a lot of passes might on the basis of the current FAQ ("as long as you maintain a Gold Card season ticket for a SWR route") use them in September next year and, because the staff have been told the third version, get into an argument on their special day out - and someone else is on the basis of the media report, the SWR forum or maybe the old FAQ, putting 15 valid passes into the bin today.
.