Not sure if this falls under conspiracy talk. What if pools have their own bots to look out for SigHash None transactions and replace them to benefit their own secret wallet or raise transaction's fee to max? In the latter case it's not guaranteed the pool wins the block and thus the fee, but it's a stealth gamble.
I don't think they have to do this, there must be enough bots out there doing it for them. Every deposit into an address with leaked private key gets emptied instantly, and they're quite literally fighting for it.