Pools mining for each other (as proxy pools) is an alternative strategy to de-risk variance. A portion of the pool's hashrate is forwarded to another pool, thereby de-risking the payout of that portion of the hashrate. Proxying reduces variance at the cost of sovereignty. Hashrate centralization via proxy pools points towards one thing and one thing only: miners and pools hate variance. Miners want to avoid block reward variance so badly only a select few solo mine. Pools want to avoid block reward variance so badly they mine for each other.