Why aren't ISPs providing stratum 1 NTP service?

From customer's point of view, getting stratum 1 service is not

a good idea. The stratum 2 clocks tend to be more stable.

I think it would be a good idea to stop providing startum 1 service
to anybody but ISPs who would then provide s2 clocks straight
out of their ciscos to customers thus avoiding the symmetry issues.

Reducing load on s1 clocks is also a good thing, as it could improve