Earlier quoted context omitted.
The alternative is the iOS update process, which has the result of non-techies complaining that their iPhone 4 is now slow after the update, and the techies they know pleading with them not to update even though the number gets bigger.
Another alternative would be to keep releasing security updates. If open source projects can manage more than three years support, it's not out of the question for Google to do it, at least for the major versions.
That's an overhead to code, backport and test. These resources could be spent elsewhere.