Oh they do! I had a choice earlier of buying an off peak return which would allow me to travel on any train this weekend, or for 5p less I could have limited myself to one train option. Thanks XC for that bargain advance offer. Laughable!!!
XC have sent me adverts offering me advance single fares for a day trip where the singles might be slightly less than a OP single, but are considerably more than an OP day return. Mind you, the GWR website tried to direct me to buy 2 singles for a Bristol - Exeter journey totalling £51 rather than the standard £34, so it may not just be them.
I have long thought there must be huge suppressed demand for XC caused by the overcrowding which can occur at almost any time of the week - it really doesn't take much to fill 174 standard class seats running between multiple major cities. If XC ever did get longer single unit trains with e.g. 350 standard class seats, I could see a rapid increase in footfall. If the trains still had the same number of staff, the revenue to cost base should surely increase - I can't imagine the operational costs would increase. That said, I have noted that if XC were to run longer trains, it might cause particular issues at Reading and Birmingham.
In any case, as XC don't serve London and aren't a regional operator, I doubt anyone will take the risk unless Parliament is moved to Burton-on-Trent.
As it is, I can see myself making greater use of the GWR services between Bristol and Exeter once the HSTs are drawn. I'm quite happy travelling on Voyagers when they're not full, but given the choice of standing for an hour or a seat for 80 minutes, I'll choose the latter. For journeys to the NW, I can see myself using the Marches Line via Newport. For the far NE, via London. That said, I only visit places in the north sporadically, so I have to acknowledge no-one in the Treasury or at XC will lose any sleep over my plans.