Streamlining. How is it streamlining? How? That's an incredibly stupid statement. In fact, this way makes more sense. You can't smack different peices of armor together as easily as you think.
You're absolutely right. Warrios of days past only used complete suits of armor and din't mix and match whatever pieces they had. For instance, you can't equip a left pauldron unless you have a matching right pauldron and if your cuirass is made of steel then the fashion police will shoot you on sight if you're sporting plain iron greaves.
And since we're talking about the ease of smacking different armor pieces together, please consider that you can pause the game mid-combat and switch from one suit of heavy armor to another. "Hold on, fellas! Yeah, I know we're supposed to be killing each other and stuff, but can you please give me 30 mins to unstrap my current suit of steel armor and strap on a suit of Dwemer armor? Please?"
In other words, please don't use any kind of "realism" excuse. Just don't. gamesas streamlined the armor pieces so they could simply design entire suits rather than work with so many individual pieces that would have to fit together and probably suffer from clipping issues. The end result is prettier, at the cost of player choice. Removing choice = streamlining. And I guarantee you that it wasn't a hard choice for the gamesas executive who made the decision, since most of the 15 million people who have bought the game thus far don't give an honest [censored] about the depth of player choice or possibly even prefer not to scrounge for all the parts in a full suit of armor.
Steamlining makes sense from gamesas's perspective and it's not inherently negative, even if it's a pain in the ass if you're into complex games. It's a giant piss down the back of the old TES gamers but they're an irrelevant minority at this point. If they like the game, great. If they don't, they can get stuffed and jump off a bridge. They're a dinosaur segment with a very limited appeal and they're deluded if they think they'll get "deep" gameplay, since it costs gamesas development time and thus money. Money they can not spend (and thus keep) if they simply shift focus to a different target segment. I understand that reasoning, even if I don't like it all that much, what with me being a member in that "irrelevant minority" segment.
Edit: Sorry for going off on a rant, mods. Happens on occasion. By the way, I rewrote the deleted sentence part after the comma, just to make the sentence end properly. Hope it's okay. Cheers.