I took Matt's advice and tried out Stratum v2 on Testnet and mined a block. It's not that difficult! Certainly the big corporate miners should be able to figure it out.
Discussion
What hardware & software did you use? How many rigs could you have supported with that setup?
I ran a #Bitcoin Core testnet node on my main beefy desktop machine and then the required rust applications as documented on the Stratum protocol website. I used an s9 but that was taking too long to find a block so I pointed an s19 at it for a bit and found 2 blocks in 30 minutes or so.
I suspect the big miners may be receiving favourable treatment from pools, maybe even being overpaid at the expense of smaller miners. It may explain their reluctance to move. I have no data to back this up, only game theory.