People who know they have broken kernels don't keep upgrading them, they stop and fix them.
People who don't know they have broken kernels also don't know they can boot with an older kernel, so they get nothing from the "backup".
We want to leave some time for people to realize their kernel is broken, so keeping three is probably just fine. Honestly, it would probably be adequate to just bump the oldest one off the queue whenever a newer one is requested. If you've got a tiny boot partition, maybe that means only two revisions. If you've got a huge boot partition it could be 20.
But just keeping them all and making people manually uninstall them gains you nothing, it's user-hostile for no reason.
People who know they have broken kernels don't keep upgrading them, they stop and fix them.
People who don't know they have broken kernels also don't know they can boot with an older kernel, so they get nothing from the "backup".
We want to leave some time for people to realize their kernel is broken, so keeping three is probably just fine. Honestly, it would probably be adequate to just bump the oldest one off the queue whenever a newer one is requested. If you've got a tiny boot partition, maybe that means only two revisions. If you've got a huge boot partition it could be 20.
But just keeping them all and making people manually uninstall them gains you nothing, it's user-hostile for no reason.