Yes... defeating the boss and advancing the game can be it's own reward.
Why do gamers need their "good job" pet on top of that in the form of 'awesome loot or it's a waste of time'... what?
I blame it on a degrading society of over nurtured children. It is the society of "participation trophies" that have resulted in the belief that without enormous praise and prizes, then something is not worthy of effort. The concept of "a hard days work is its own reward" is completely alien to them.
Here is the funny thing though. The most pivotal encounters in a game, the final encounter, the last fight or culmination of all the effort in a game... provides no loot of any real value (ie you can't use it for anything, the game is over, the reward might as well be a note that says "thanks for playing!).
I guess they shouldn't bother with the last fights in these games, you know... its all risk, no reward, not worth playing. *chuckle*