Reward for region completion
If they were to only give out items usable by your current character you would not necessarily get the stats you want or the weapons you use, besides if you’re lucky with the exotics in the higher leveled areas you could sell them for a few gold and buy the items you want instead.
Personally I don’t have a problem with it, everything else is random and the things that aren’t you have to pay for. I think it kinda makes sense