First it’s pay, no ads. Then it’s higher tier for no ads. Then it’s higher tier no ads but watch a trailer at the beginning. Then it’s higher tier and ads.
In some cases, yes. I specifically don't use Spotify in part because I can possibly lose access to my playlists and music I listen to in the future. Building a music collection is a big part of listening to music for me, so the future possibilities of the service actually degrade todays product.
I don't watch streams so I don't have any input on Twitch, but I could imagine someone having a similar outlook.
I don't think you lose access to any of this when you unsubscribe, I think you just start seeing ads again when watching the live stream.
I'll happily pay for things like LWN, though, even though I'd get everything ad-free two weeks later anyhow.