Think about it.
Most of you take an enhanced level of interest in the railways, have a great deal of technical knowledge and understand how the ticketing system works. Most people don't however. So many people don't understand the concept of through tickets for example and genuinely believe they must buy a seperate ticket for each leg of their journey.
TOCs will struggle to complete with The Trainline, because their branding turns potential custom away. TOCs plaster their own name all over their websites, the URL and the result is that the many people who aren't technical experts on ticketing will only think to go to their website if they are making a journey involving one of their trains.
Now most people don't want to sign up to loads of different TOC websites. The Trainline is a household name without the branding stigma of being allied to just one TOC. People know they can buy tickets nationwide on that site and this will drive loyalty. People will pay the booking fee for the perceived convenience of being able to buy all their tickets in one place.
A die hard value seeker like me wouldn't touch that website with a ten foot bargepole, unless I got something out of it like enhanced levels of cashback or oodles of points...
Completely agree with this:
-Lots of people don't realise you can book any journey on any TOC's website
-They've got their brand name spot on. Easy to remember, and was one of the first brands put out in the late 90s when online booking first became a thing, and its been stuck in the public's consciousness ever since.
-They're the only one to advertise on TV nationally. Any TOC adverts tend to be regional only (possibly Virgin Trains excepted in years gone by).- for.example our local cinema shows Greater Anglia adverts before the trailers.