Three things affect my decision to use non-real names:
1. Most of the vehicles I'm drawing are 'inspired by', not accurate 'representations of'. The articulated dump truck is a blend of Moxy, Volvo, Cat, JCB, John Deere. The mining truck is a mix of 25 years worth of big mining trucks. Therefore it's mostly not meaningful to say it's a Volvo XY3423B or whatever when it isn't.
2. I am re-balancing vehicle stats for gameplay, therefore I don't want people popping up and saying the Cat D6 wasn't 200HP in 1974, it was 203HP. And the top speed is wrong... etc." -
because it's not supposed to be a Cat D6. Basically 'wrong' stats disappoint some players (I wouldn't like to see a 5000HP SD40 in CanSet, it would be just wrong), and I need the freedom to make balanced gameplay.
3. The legal issue I can't duck. Company names are trademarks, and all it takes is an aggressive legal team to get into legal disputes. Although the most likely thing is a cease-and-desist letter (which could be complied with), if a lawyer wanted to take it further they could. For a private individual they are very unlikely to pursue it very far, but for various reasons, they could
definitely come after my company on this issue; I can't afford that (legals take up time and money, even if it's just a cease and desist). And yes
it is free advertising, and there is no damage to the brand, but IP lawyers don't see it that way - they make their living by taking the opposite view.
Even brands that should get it often don'tSo sorry, no to real names, because
they're not real vehicles, and
I don't want the hassle. 
I know that won't please everyone, but it gets the issue out of my way and lets me get on with drawing the set - in my view the best sets are made by just a few single-minded people choosing to do something and sticking to it
