I suppose if I got into it I theoretically could watch and enjoy competitive games. Not the same as streamers playing singleplayer games though.

There are streamers who dedicated their lives towards a single game and become incredibly proficient at it. They don't go pro either for monetary reasons (streaming could be more lucrative) or there just isn't a pro scene for that particular game.

You could learn A LOT about various mechanics aspects from watching people play Minecraft. You can learn a lot of tricks and map knowledge from watching FPS players. Or it could be just a variety streamer that's incredibly funny, like Soviet Womble. Etc., etc.