CSX is notorious for this. If you ever look at some models, actual models that is, they have a note for any CSX or CSX predecessor fallen flag designating it a CSX licensed product or something like that. TS2014 finally got a license a few months ago to put CSX equipment in official releases long after every other North American fallen flag. They've even asked for royalties and licensing fees for freeware. There's something to be said for protecting your brand, but they take it too far.
Back to the original topic though, my biggest complaint with the fictional stuff is that it seeps, dare I say invades, into completely unrelated threads. It's annoying to have Thomas shots crop up in between complex prototypical scenes or constantly comparing every UK steam engine ever to the Thomas version. Or someone asks about a station or shed and someone responds with an object lifted from a fictional universe with nothing in common with reality. Also, these things are associated with young children, that is less than 8 or 9ish and that's really pushing it, well below the minimum age to join these forums. I've seen some people using Thomas Trainz stuff for their kids and grandkids, but these aren't the types usually posting it in every thread. Finally, a lot of the fictional stuff is obviously dated or of low quality given the niche market it fills so it's not even nice to look at for people who don't enjoy it. This isn't even talking about putting stuff that is entirely non-train related, I'm looking at you Bronies, into unnecessary situations.