This is all Apple's fault for demanding 30% of their revenue from IAP.
> subscribe in a way that Apple has no control over
What is the benefit of Apple's control, though? That is the main question.
> I fail to see how this is not user error
It was user error. It's a very common user error, forgetting to cancel a trial. You're missing the larger picture here, which is that Apple publicizes and justifies its App Store lockdown and cut in terms of consumer protection, claiming that App Store is a very safe place to find and buy apps. If Apple cared about protecting consumers, it would protect them from common errors such as forgetting to cancel a trial. After all, Apple does "protect" consumers from the common error of installing software that they shouldn't from the internet, by completely banning internet app installs on iOS.
No, the most profitable company in history doesn't get to play dumb. At Apple's scale, Hanlon's Razor does not apply, because there's no effective difference between incompetence and malice.
The ostensible protection that Apple is providing is from subscriptions for which cancelling is difficult. If the subscription happens through the app then it's found in the same location as every other subscription that's made through any other app.
I believe OP's point with their quote ("I fail to see how apple has any responsibility ...") is that with the given examples (Netflix, Spotify) one cannot subscribe using their iOS apps. The user will need to go outside Apple's ecosystem (netflix.com, spotify.com) and subscribe in a way that Apple has no control over.
At any rate, I fail to see how this is not user error given that you are sure this is not an app which had its subscription made outside the App Store. If it was made in the App Store, the user is only required to remember to cancel at all.
I don't mean to speak against most of what you're saying but many of your arguments read as a non sequitur. It's hard to agree or disagree because it's just hard to follow along.
(edit: rephrasing)