There are 2 questions here:

1. Why not stratum v2 right away?

I'm not an expert, but maybe miners need to upgrade their firmware? Well, some sort of software upgrade must happen, maybe they are not ready?

2. Why not Kano pool?

Miners seem to prefer FPPS to other payment schemes, which makes sense, due to the steady stream of revenue. Since Kano only finds one block per year, I don't see how it could offer FPPS to its "customers", so in that regard Kano pool will always be behind bigger pools. So, in this particular question, size matters 😉

Again, not an expert, just thinking out loud.

https://originstamp.com/blog/pps-vs-fpps-vs-pplns-vs-pps-mining-pool-payouts/