Also - “windows does it” is obviously irrelevant when we are talking about a mobile OS.
I won't continue this discussion about maintaining compatibility. This is fundamentally a philosophical issue. I agree with the sibling comment that it is the job of an OS to provide stable APIs across versions. It requires some effort (as a long-term library maintainer, I'm very well aware of this), but it is not an impossibility at all.
The job of the computer is to serve the end user. The job of the OS is to manage the computer’s resources on the users behalf.
API stability can contribute to that goal, but this is not an absolute.
Apple balances their view of what is good for users over what is good for developers and themselves.
Your preference is to prioritize developer comfort over both end users and Apple.
If you think there are no insecure or inefficient APIs in older versions of operating systems, then you are simply wrong.
API stability sometimes serves the end user, and sometimes does not. When it does not, it should not be maintained.