Non disruptive ads were meant to advertise.

Slightly annoying ads were meant to be seen more since people just ignored banners by default.

Hidden ads (like an ad in an article which you really could tell it was an ad) were meant to increase the image of a company.

Disruptive ads like in YouTube or Spotify aren’t meant for advertising. They don’t really care about the advertising money, they want to force you to buy premium. The more annoying the ad is the higher the chances you pay 20€ a month for them to go away.