Why are people so obsessed with quick grinding?

I don't understand the point of it.

You look some guide up only to grind a camp as fast as possible to then do... what exactly?

I have this one friend, and all he does is look up guides on how to quickly unlock everything in the game. Once he is done, he has nothing to do and stops playing.

Like, I really try to understand it, but don't you see that it's pointless? It's nice to have the motivation in the back of my head when playing, but there is no point in rushing it.

I feel like these people would grab the first opportunity they get to unlock everything all at once if there was a glitch to do so.

It's just a mystery to me.