Their marketing is good. Even to this day if I want to find train times I automatically type in their url, and then remember I need to go somewhere else to book it once I get to that stage...
I do the same, but with SWT's journey planner. That too is a Trainline clone, and remember that SWT's owner's are Stagecoach who own 49% of Virgin. I'm just used to the Trainline display of results, so it's convenient for testing out routes, times and fares.
Once I've decided, I go over to FGW, where I get Nectar Points!
The really aggravating factor is that there are minor but annoying differences in what the different TOC websites will offer on different routes.
It would be nice to have a 'Sticky' which listed all the websites and told us which ones charged and for what, plus which ones offered perks. Further up someone mentioned that Trainline, RailEasy, and Red Spotted Hanky charge fees. Of the TOC offers, I am only aware of East Coast which gives points (redeemable for tickets, other offers, wifi passes and First Class Lounge passes) and FGW which gives Nectar Points.