I made a similar comment up-thread. In general the train simply doesn't compete on convenience until the journey is long enough to require a stop for a meal. Even then only if the journey involves limited lugguage.Paris to Lyon is 305 miles compared to 200 for London to Manchester.
There is a clear time advantage for the former by train as a TGV - but as I understand it TGV journeys are limited in that you have to travel on your booked train etc.
City centre to city centre makes sense by train - but most people aren't travellimg city centre to city centre - if you were travelling from somewhere like Hemel Hempstead to Ashton under Lyne - you'd end up with a much longer train journey than a simple Euston to Stockport / Piccadilly at which pointdriving it is more attractive.
To even think about competing on door to door journeys of up to three or four hours the off-peak walk up fare needs to beat the marginal cost of driving.