Many people do have problems with it, for whatever reason.
My view is part of the reason is when Advance tickets are offered for sale on services that are effectively turn up and go. For example my local line has a fast service to London every 15 minutes. When there is a service every 15 minutes people then think they can get any train - what is point of advertising that trains run 4 times an hour when you can effectively only catch one specific train.
I imagine on long distance routes, you get the opposite of people buying flexible tickets but believing them to be booked train only, since for someone used to flying the idea of a ticket that allows you to walk up and take any Glasgow to London train via various routes would be quite surprising, especially when it's not much more expensive in a lot of cases.
However, these people are obviously not penalised and therefore we don't hear anything about it.
If it was up to me, I'd have a small charge (say £5 on short routes up to about £20 on long routes) for people travelling on the wrong train with an advance ticket, along with a clear explanation of the different ticket types - that way anyone doing it as a genuine mistake isn't heavily penalised, but they are incentivised to learn the rules and adhere to them in the future (if you just let them off, they'll take their chances and do it again). Anyone who is caught doing it frequently would then be much more severely punished as that is then clear deliberate rule-breaking. It would also mean if say your bus to the station is super late causing you to miss an advance train (i've been on buses over 30 mins late and missed trains as a result), you could pay a little extra to take a later train, but once again if you did this too frequently then it would seem suspicious.
