Kill the dragon, get its horde. It's an idea as old as gaming. It's an idea as old as capitalism. Hell, it's an idea as old as *fairness*. People want something to show for their effort.
The starting argument was that killing the final boss and getting the loot is pointless since the game is over.
As for any relatively minor bosses loot and questions about loot rewards in general:
If you go down that road then getting the loot becomes the primary purpose of playing. Then that purpose distorts the whole game because every other feature becomes secondary.
The mindless, unspecified, general nonsensical notion of "fun" and "entertainment" becomes the holy law and everything that may bother that cheap, superficial feeling is deemed an enemy of that "fun" - and then you have screaming hordes from body snatchers taking over.
- Current state of civilization popular culture, btw. And it would be the state of the whole civilization if it wasnt for individuals resisting.