Main exception would be business travellers who may indeed buy flexible tickets for long distances.
I really don't think so. Business travellers are, in my experience, able to schedule their meetings and are under pressure from their expenses departments to use the cheapest ticket - if I ever used something other than an Advance I would get a "please explain".
In contrast, most people travelling at their own expense, whether that is for a leisure activity or on personal business, do not know when they are going to travel, and in particular when they are going to return. There are as many reasons for this as there are people travelling - you may decide to spend longer, or less time, on a visit depending on the weather* - the football match you are watching may go to penalties - the country walk may take longer, or less time, than expected, or may be cut short by the weather - the trial in which you are a witness may take longer, or less time, than expected for you to be called - an emergency dash to a hospital bedside cannot be planned in advance, nor can you know when you will be able to return. Who is going to take the risk that there will be no affordable "advance" fares left by the time you know when you will be going home?
LNER's abolition of regulated walk-up fares is of dubious legality, and if allowed to continue (let alone extend to other routes) will mark the end of the walk up railway, and drive more and more people on to the roads.
* I have seen proposals to abolish off-peak fares on all journeys longer than 70 miles, which puts even a day trip from London to Margate out of reach.