Does documentation necessarily create such an obligation? That would jeopardize most open-source projects, most of which explicitly promise no warranty.
Apples licenses for these will include very strict NDA clauses that make it impossible for apple to share the documentation they are provided but that vendor.
I don't want my speakers to stop working because I stopped paying subscription.
I say this as a longstanding iPhone user, and up until recently, Mac user.
Sometimes backwards compatibility is preserved even to the point of preserving bugs (especially if the companies/apps depending on it are large):
https://www.triplefault.io/2017/07/breaking-backwards-compat...
https://arstechnica.com/gadgets/2008/11/ars-investigates-doe...