I imagine that this approach comes down to a balancing issue. As you pointed out Rag, there's a number of vendors you can aggro and have to kill purely in the course of playing the game normally. Which means Larian would need to balance the difficulty of their combats around players getting a lot of potentially powerful gear. And if we include your suggestion about quest rewards then that could get even worse, because then that would mean a bunch of occasions where our character could get two different potentially powerful reward items if we have to choose between supporting two factions again like we have here in act one. To avoid that they'd have to find ways to justify them not having the item anywhere we could easily get to it,which could hamper their writing.
I don't have much of an opinion on this aspect of things in general because I really don't care about loot and probbly would not have noticed this if it hadn't been pointed out, but the way I see it, this is a game and Larian made a choice that they think benefits the game mechanically. I've always been a beleiver that fiction doesn't need to make any kind of perfect sense, and I've never liked people using the term 'gamey' as a negative just on principle. It's a game, it's gonna be gamey because games should be fun and enjoyable, that's more important than adhering to logic. Those two things aren't mutually exclusive and indeed sometimes adhering to logic does make games more fun. Larian clearly didn't think this was an occasion when that was true.
