Mediocrity should NOT be the standard for players in any content.

[SturmChurro]

Look at what SturmChurro said.
But also, with that logic. Would you work a 9-5 job with no pay? Would you plant a large amount of seeds in a football sized yard for it to never grow?
You accomplished something, you worked for 8 hours and was productive. Wouldn't you want something for all your hard work? No? you want to work for free? man.

Well, some people do get a sense of accomplishment from going back and completing content for no reward, the reward is the experience itself. You are opening yourself to a counter-argument. Different people like different things, I am just impulsive. A good reward is always something to keep people motivated though.