I'm not going to watch the video right now or get angry since it's probably just a poorly conceived "stereotype and over-simplify subject X to get reactions out of community/person Y" joke that tends to be all the rage these days, but I personally watch let's plays and such because:
-Sometimes I either wanna see what a game is like before playing it, or I don't have the money for a game right now so I watch some footage of it to quench my thirst for the game.
-I like to see competitive players and speedrunners be amazing at the game, and if it's a game I love to play, I take mental notes from that to improve my own play.
-Regarding games with a modding scene, subscribing to a channel that specialises in showcasing mods for a game is a good way to keep up to date on what kind of mods are available.
-In single-player games, sometimes watching an LP from a dedicated and knowledgeable fan of a game/franchise can lead to you discovering secrets, tricks, or trivia regarding the game that you may not have discovered yourself.
-Walkthroughs are just helpful and help you progress through a game. Videos with commentary are the best format for that as they can provide the most accurate info easier than other formats. This is pretty much required for a lot of old games, and even with a more modern game like Kingdom Hearts for example, guides are helpful for figuring out the fastest way to get item synthesis materials and what not, stuff that's pretty much impossible to figure out on your own in a reasonable amount of time.
-There are certain LPers I watch dedicatively because I just really like the people. This can be because they present their content in a creatively pleasing manner, they are smart or have a good sense of humour (better than Kimmel's, in a lot of cases

) making them entertaining to listen to and watch, etc. I tend to watch LPers that seem to have similar tastes to me simply because I don't really have anyone like that IRL and it's nice to hear someone with similar views to me on gaming every once in a while.
-LPs are good for research purposes as they can be an indicator of a game's popularity/infamy, or can give you an idea of people's general opinions and interpretations of certain aspects in a game. For example, there are an alarming amount of people who misinterpret Rosalina as being a princess (among other misinterpretations about her), which I see a lot in YouTube videos and comments sections. And it's kinda interesting to watch phenomenons like that play out.