Doing nothing is still a choice, and will result in their stake being slashed in the non censored "fork". If socially the non censored chain is deemed legitimat

Doing nothing is still a choice, and will result in their stake being slashed in the non censored "fork". If socially the non censored chain is deemed legitimate, this is a negative outcome that cannot be undone - hence a "commitment". Without slashing, miners do not have to make any commitments - their funds are duplicated in both chains and they can switch to mining whenever they like.