They will be on season tickets or travelcards.
Season tickets of course being the cheapest
A peak time return from Crawley to London costs £58.80, or 52p per mile.
A weekly return is £121.40, which for 5 days travel would be £24.28, or 21p per mile.
For making things revenue neutral, getting rid of weekly season tickets and just charging a fare for the journey seems far better.
Also, in a national railway system, why should Birmingham - London passengers get 17p per mile, but Birmingham - Exeter get shafted with 37p ?
Because theres lots of capacity and competition between Birmingham and London, but there isn't between Birmingham and Exeter.
You could increase investment into track and rolling stock to improve that situation, but that isn't accomplished by reducing prices on already full trains (and thus rationing the space in a different way). Personally I'd do this by increasing the costs of rail on regular users so they pay the same as occasional users, and using that extra revenue that to make things better for occasional users.
Of course we're getting rid of competition so expect the more affordable trains (like the west-coast mainline) to become as terrible as the east coast soon enough, pushing out occasional users. Yeay.