I compare that to Windows which has been around two decades longer than iOS and Android and which APIs have remained remarkably stable and backward compatible. It is possible to do it. It is just more work.
Well, to be fair, this comes at the cost of Windows (like other major desktop operating systems) being considerably less secure than Android or iOS. This tradeoff is not easy to avoid except by designing the permission model to be sane from the start, and we all know that good upfront design doesn't exist.
Legacy baggage also comes at the cost of performance, which in the case of mobile devices, means reduced battery life.
As an app developer, it's immensely frustrating to have to keep updating apps to stay on top of the latest SDK.
As a mobile user, I delete apps that get flagged up as battery hogs.
So that leaves me with a fairly simple choice, and I keep stuff updated if I expect anyone to keep using it, and if I abandon it, I shouldn't be surprised when my users do the same.
That's not really being fair; Windows was created decades before Android (one decade if you only count NT). The security model is different, because it was created in a different computing era.
I think the difference in API stability is a result of the different financial motivations between Microsoft and Google. For Microsoft, the OS itself was the product; to not make the APIs backward-compatible would have meant significantly less revenue and market share.
For Google, the OS is not the product. Google doesn't make any less money when someone continues to run an old version of Android. There is no monetary incentive to make new versions of the OS API-compatible with older versions, nor is there any monetary incentive to make new versions of the OS run on old devices.
Consider also that the cost of upgrading to a new (non-flagship) device in 2019 is much cheaper than in 1995. A typical PC circa 1995 could cost $2000 or more (price adjusted for inflation). Today, you can get an entry-level mobile phone for 1/10 that price. Back then, a family might hold on to a computer for five or ten years, because it was so expensive to upgrade. That makes paying $100 or so for an OS upgrade every few years worthwhile, because it's much cheaper than buying a new PC.
Arguably the pros of just making security the users problem outweigh the cons of trying to protect the foolish from themselves. The desktop ecosystem for all its security problems is rather vivid
