I think that condescending attitude stems from the fact that in the world of model cars, there are just way more kids and/or "unserious" modelers building donks or wild customs that would be totally impractical in the real world, people who continue to ignore obvious mistakes like the "magic floating alternator," etc. than there are "unserious" armor modelers. And I think that many (most?) serious/hardcore armor guys see their way of modeling as being harder, more demanding, more challenging, and requiring more skill than the guys who put giant wheels and sparkly paint on a car (no offense to those who do... I'm making a point). I mean, comparatively speaking it is a lot easier to throw together a bunch of parts box pieces that may or may not make sense in a real vehicle and say you are being "creative" vs. the discipline it takes to do the research and take the care to build a perfectly accurate model of a specific Panzer from a specific theater or a specific battle, etc. Not that all car modelers build that way, but enough so that it has become the stereotype. See what I mean? It's no wonder that a lot of armor builders look down on model car building as a kid's game.
I'm not saying I necessarily agree with them, just trying to explain where their condescending attitude comes from... and when you think about it logically, it's actually pretty easy to see.