Because it circumvented upkeep in a way that was not possible to solve easily (i.e. if you don't own the weapon you can't pay to repair it).
I remember paying upkeep for things I've picked up, but I have no evidence so...
I don't regard this as a real problem though. You only got to keep the weapon until you died... and it was a neat way to get to try out items that you couldn't afford. Scavenging near the end of a round for something to fight with next round was a neat thing you could do, and now it's gone, and that's kind of lame. Oh well.