Mining isn't exactly that centralized and even if it were they'd only really be able to roll back the most recent block. That's nothing like general chargebacks, as it would be one-off thing and only be in effect for 10 minutes, and is heavily disincentivized as it would destroy the reputation of the miner.
The difference with legal contract enforced systems is they aren't. No one is going to build a system that restricts it's owner legally, and furthermore legal rules are leaky abstractions that have workarounds and spotty enforcement.
The difference with legal contract enforced systems is they aren't. No one is going to build a system that restricts it's owner legally, and furthermore legal rules are leaky abstractions that have workarounds and spotty enforcement.