Personally I think the problem is just our need to consume everything as fast as possible.
Content being spread out means you use one for a while, then switch, the content won't run away (unless of course HBO's new CEO has something to say about it).
But it's us, we're the problem. Like for example, you have Game of Thrones back on HBO and you have Lord of The Rings coming up next week on prime. Logically you subscribe to one, watch one, then cancel and switch to the other.
A lot of people just can't do that, they must watch both as fast as possible, they must consume the content the moment it releases.
That's the beauty of streaming services. No forced ads, watch whatever you want whenever you want, and no yearly forced on contracts.
Sign up to 1, consume, cancel, sign up to 2, and keep it up.