I was there from 2011 to 2019. We had pretty clear numerical guidelines for continuing support of a platform or OS. If the numbers are close, things like upgradability or difficulty of support make a difference: if all the devices running OS 1.1 can actually be upgraded to 1.2 and 1.2 fixes important things, then dropping support for OS 1.1 can happen with more users still there.
If builds need to be signed by the OS maker and they won't sign any more builds, user count doesn't matter (sorry Nokia S40 and iPhone 3G).
We did make some longer lasting builds for platforms we were ending support for, but there needs to be an end. Older clients don't support newer features and we didn't want to have a network where that was the status quo. I don't know what the current expirations are, but mandatory updates a couple times a year helps keep the feature support similar.
If builds need to be signed by the OS maker and they won't sign any more builds, user count doesn't matter (sorry Nokia S40 and iPhone 3G).
We did make some longer lasting builds for platforms we were ending support for, but there needs to be an end. Older clients don't support newer features and we didn't want to have a network where that was the status quo. I don't know what the current expirations are, but mandatory updates a couple times a year helps keep the feature support similar.