Now I'm not any fonder of the cookie cutter armor and undyeable stuff than anyone (actually I really hate that sense of sameness) but I did have a thought about why it is.
Many many moons ago (going on 30 years now so my memory may be faulty here) I used to play a table-top game involving armies of little 25mm lead figures. I am no longer certain it was Warhammer, but it was something very similar if it wasn't, and it WAS played with lead miniatures. LOTS of minatures. Lots of hand painted miniatures. And one of the rules I remember was there were two kinds of troops, regulars and irregulars. If your miniature army was painted and painted each company alike, they were considered "regulars". If they weren't painted with at least two colors or painted up in different colors, they were "irregulars". And "regulars" were much stronger and better than "irregulars".
Since Warhammer's based on a tabletop game of the same type, it's possible the armor and stuff looks so cookie cutter because the minatures they are basing our templates on all looked exactly alike more or less, and all had to be painted alike. So it is technically part of the "lore" of the game that it's so.
On the other hand, I believe there are times when you can and should chuck the lore out of the window to make an adaptation of something more fun. And something as minor as armor coloring all alike is definitely something that should be tossed out for the computer game.