That's because it's an unconditioned stimulus (classical conditioning theory). If you repeatedly watch their videos, and like them, you'll start to associate their intro animation with the content you like, and you'll like the intro animation. Later, you'll even come up with post-rationalizations for why it's not quite so loud or useless.

Unless of course you're so turned off by the intro that you bail out before giving their content a chance.

The TED intro (standard series) bmakes me gag now Ten seconds.

Mind, mobile YT doesn't have keyboard sip, but mpsyt does.