Why do all YouTubers beg for likes and subscriptions? Including celebrities like Jimmy Kimmel. Isn't it obvious people will do that if they like the content?

Because subscribing means you'll know when they release another video. YouTube only gets payed when soneone watches an ad, so YouTubers only get payed when someone watches an ad on one of their videos. So, they need the maximum people possible to watch ads, and they have to account for people using ad block or skipping the ad after 5 seconds. It's usually their entire livelihood. The entitlement and bitterness of thinking that people don't deserve their livelihoods because they have to openly ask for them is saddening. They provide you (or at least others) with entertainment; the least you can do is let them ask for you to at least consider subscribing.

/r/AskReddit Thread