I mean, Ultimately, You're investing time and resources to kill all the zombies and loot the building, and then time and resources to kill all the zombies and loot it again- You can consider that double dipping to be OP, but, It's not terribly different from killing and looting building A, then walking 30 blocks to building B and killing and looting that one too. Saves you what, 15 seconds?
The quest resets ensure there is always a steady source of any given material, even in long running multiplayer servers where after the first week or two with 4-8 players, basically everything in the map will have been dismantled leaving nothing for anyone who joins later.
The resources it gives you access to aren't even difficult to find, You can get to day 100+ with ease off of stripping down a single city without ever doing a quest- You can go door to door to door killing the zombies and stripping out the electrical and mechanical parts and achieve basically the same thing. But without quest resets you WILL run out of those parts eventually, Meaning that for players who plan to play for a very long period.
Iuno.. I guess I just don't see it as much of an issue personally, since it really doesn't give you much of an edge at all over just going door to door. It's kindof like that infinite clay 'exploit' that's been in the game forever and the devs don't see a reason to bother fixing.
For those not in the know, if you have motherlode you can craft a clay block with like 20 clay, then dig it back up with a shovel to get 25-40+ clay. Effectively getting back more clay than you spent crafting it. But, while it is in fact an infinite source of clay, you need to spend the time digging it up anyway, and you further have to spend the time crafting the blocks to do so. And given the massive abundance of clay floating around, doing this is basically no different from just going outside your door and digging up clay with the exception that you don't leave a giant world hole in the ground. :P