I know a lot of people disagree with me on this, but “just” the intro to a show is still an ad.
I absolutely hate ads and I hate “intros” to shows. They are one and the same. I don’t care if I have the option to tap a button to skip the intro (some services don’t even allow this), end of day is I literally pay for “ad-free” content on these services and they still manage to mess that up.
I’m open to hearing why people are ok with these intros while not ok with normal ads.
With HBO, it's usually an ad for another one of their shows, rather than an ad for the thing you're already subscribed to. I'm okay with that, even though I usually skip the ads anyway.
Sometimes, I like the intro. The music, the visuals, sometimes they get you in the mood for the show. Sometimes, I just want to get on with the show. I appreciate having a choice.
Intros on a serial show are expected, and in some cases change subtly from one episode to another to provide additional entertainment value (eg the Simpsons intro). In other cases a change of intro sets the setting for the episode (eg Star Trek: Enterprise's Storm Front episodes).
YouTube ads are not related to the show, provide no contextual value, and in the case of interstitial ads are not even at a predictable time. They also tend to be inanely repetitive, showing the same ad over and over in consecutive videos. Contrast those to eg halftime ads at the Superbowl broadcasts, which have predictable timing, variety, and have a history of being (or trying to be) entertaining.
Because on Netflix what you're skipping is something you expect and maybe even want to see. On YouTube it's ads, which you don't necessarily expect nor want to see. And the skip button is just associated with that.
Also, on YouTube you sometimes have to skip multiple consecutive ads, sometimes you have to wait for a few seconds, and sometimes you can't skip them at all. It's not made to be practical, it's made to serve you as much ad-time as possible, as that is the bread and butter for YouTube (contrary to popular belief they don't make a lot of money, so it makes sense. Although I'm not sure I like they way they try to make money to stay in business).
Videos haven't had a single ad in years. It's always multiples bunched together and inconsistent as to whether you can skip or have to wait it out. Shows only ever have one opening (sometimes an ending as well) and their less predatory.
I think they use that to help track whether you're watching or not (I don't recall ever seeing the "are you still watching?" prompt when skipping intros... but my sample size is 1)