For streaming services to be profitable, ads are necessary. Netflix said for over a decade that they would never put ads on their service. They had one bad quarter and they quickly decided that they were willing to change their minds in order to create a new revenue stream.
As far as your Disney+ point, you're right that Disney+ in the US is weak, but I have a feeling that on Disney+ Day and D23, we're going to hear about a lot of general content and more binge offerings coming at the very least by the time ads come.
Ads are most useful on Television series and it's been proven that while new content is good, library content with a ton of seasons is what most people watch on streaming. Disney owns a ton of this type of stuff. New Girl, How I Met Your Mother, Scrubs, Modern Family, Black-ish, Grey's Anatomy, Lost, 911 (and 911: Lonestar), It's Always Sunny, The League, Family Guy, American Dad, Bob's Burgers, Futurama, King of the Hill, etc, etc, etc.
Most other countries already have the Star tile which includes all of that content and has for a year and a half. The big problem with the US is Hulu. Disney needs to buyout Comcast's 33% in an early buyout deal and just integrate Hulu into Disney+ and the price would for sure be worth it. I still think at $7.99 with ads it is. $10.99 though for no ads and a service that is still growing up isn't worth it. Of course, i'd pay it because I hate ads and since I use a VPN straight from my firestick, I never, ever use the US version of Disney+ and it's one of my most used services because there's actually a ton to watch.