I don't know exactly how ETH works, but it seems like with bitcoin there could be a risk like this:
You send your huge-fee transaction secretly to your co-conspirator miner. They start trying to include it in their blocks, and eventually get one (call this block X). But now your transaction is not a secret anymore, and so another large miner can decide to keep trying to mine off of block X-1, but including your transaction. If they can outpace your miner (maybe by spinning up extra compute), they will produce a longer chain in which the $23M goes to them instead of your intended recipient.
It seems like a very large mining fee would change the incentives that are supposed to keep miners all working on the same chain.
You send your huge-fee transaction secretly to your co-conspirator miner. They start trying to include it in their blocks, and eventually get one (call this block X). But now your transaction is not a secret anymore, and so another large miner can decide to keep trying to mine off of block X-1, but including your transaction. If they can outpace your miner (maybe by spinning up extra compute), they will produce a longer chain in which the $23M goes to them instead of your intended recipient.
It seems like a very large mining fee would change the incentives that are supposed to keep miners all working on the same chain.