If all the trains were full, then they surely wouldn't be in any financial distress as there passenger numbers and growth would be far higher.
Whilst there are a lot of XC trains that are overcrowded, particularly during the peaks, there are also many of there trains that arn't overflowing with pax where extra advances would help attract passengers,fill the seats and might help there revenue situation just a little bit.
For example I was on a Stoke-Birmingham service on a Saturday afternoon not too long ago and it was no more than 50% full.
Therefore if XC had attempted to fill some of the seats with cheaper advances on the service (less than the £15 Tier 5 Advance) which up until a few weeks ago was the norm, making it higher than the price of a SVR for returning passengers, then it would have increased revenue on that service.
Presumibly XC have picked up on this and realised as prices have recently reduced on the Man-BHM corridor with cheaper £5.50 (Tier 1) /£10.50 (Tier 3) tickets appearing more frequently, which is a welcome step in the right direction to helping there finances , even if it still doesn't go far enough to help them achieve the passenger growth and passenger numbers they originally forecast to achieve, and which there whole franchise is based upon.