>>63907805
Magwel in AR-15 is byproduct of the initial 20 rounders that were supposed to be single use. AR-15 mags are lightweight and kinds fragile. Magwel was supposed to surround magazine and protect it from bumps. Also magazine's locking side notch is much easier to manufacture (compare colt magazine with AK-47 magazine made from multiply parts), remember AR-15 magazine were supposed to be single use!
But then single use was abandoned, straight 20 rounders replaced by curved 30 rounders that somehow are supposed to fit into straight well. And magwel is grandfathered. Huge mess.