Also, because we understand neutron degeneracy pressure, but don't yet know what (if any) quantum effect would prevent an actual singularity from being reached

Also, because we understand neutron degeneracy pressure, but don't yet know what (if any) quantum effect would prevent an actual singularity from being reached once the upper limit of a neutron star was breached. There is speculation that quark matter and quark stars may exist but no evidence of it yet.