Most people are not put off; most trains are pretty full. They are maximising revenue, not maximising seat utilisation.
And it works: you are prepared to pay £250. I will pay maybe £80 for the same journey. The company gets both fares. A small number of people will drive instead, which means they can just about get away without lengthening their trains (which is expensive).
You want them to reduce the price for businesses; that isn't going to happen unless Government increases subsidy, which isn't going to happen!
Your post demonstrates how XC are doing the optimal pricing to increase revenues while avoiding too much overcrowding.
I accept that XC are looking to maximise revenue based on their existing capacity and I don't mind them charging full wack to businesses. However:
1. The route competes with car travel more significantly than long distance services to/from London, so you would expect more elasticity in the fares compared to London as passengers have other options.
2. This isn't actually the case. Two months out, the advance fares for most trains are not significantly lower than the walk-up fare, whereas London fares show much more elasticity.
3. The route is usually heavily overcrowded.
From this I'd conclude that there is significant suppressed demand on the XC route. Given the quantity of rolling stock coming off lease in the near future there must be a real opportunity to improve capacity at relatively low cost.
Anyway, my original question appears to have been answered - the fares policy is deliberate. Looking at the advance fares around the end of the summer, there is a clear weekend / weekday split, but there doesn't seem to be much adjustment for weekdays during holiday periods. One would imagine a more detailed yield management algorithm would identify this and look to maximise revenue accordingly.