Miners only have the task of organising the blocks. If miners use software that violates the rules of the network, a fork is created. Miners cannot run any other software otherwise they are no longer part of Bitcoin. Also, there are miners who will not follow this and make a lot of money from it.

A softfork does not violate the rules of the network though, that is the difference between a soft fork and hard fork. Miners are free to choose what software to run the same as any other network participant. If a minority of hash power doesn't follow it, the majority chain will always overtake the minority fork. So any miners that don't follow it will lose a lot of money.