@Caedem likely not how it works. The 3.5.1 was the last xenial release. Those 9k focal devices, are those who moved from xenial to focal. So there would be a bit less than 4k xenial left with numbers shrinking.
And we need to drop them for security reasons at some point. Or can you justify providing a unmaintained insecure system? Also some older devices will simply die due to hardware breaking.