It's never made sense to me that not only do we have to pay for the right to do some menial chores, but they can also expire.

I know, right? If we're doing something for someone, they should be paying us, not the other way around. It's one thing if the bounties are stored on some sort of bounty clearinghouse where they are vetted first: then I could see an in-game reason to charge Guardians glimmer or something as a fee to that clearinghouse in return for them ensuring that all the bounties are on the up-and-up... but I somehow doubt Bungie thought that deeply into the concept, in character or otherwise. :P It's just a pointless excuse to make players use up their glimmer to perpetuate the grind.