Miners can't just go and change the protocol. They risk that non-miners won't accept new blocks, so if they are going to enforce different rules, they need to m

Miners can't just go and change the protocol. They risk that non-miners won't accept new blocks, so if they are going to enforce different rules, they need to make sure that everyone (not only other miners) will be okay with that. Of course, some people can upgrade blindly. But if in the middle of transition it turns out that some people are worse off, everyone will rush back to avoid wasting resources on blocks that are not 100% accepted.