as someone who does that.......i can explain XD
i think for the case of minecraft is fun to see what other people build and what shennanigans they get into....and some youtubers can be hillarious,
guess is like watching a friend play a game?
also, you can learn how to do things you didn`t know were possible.
i started maining Pacman in Smash thanks to a badass montage of the crazy things he can pull off with his moveset XD