The current fork of eth is programmed to kill itself sometime next year. This means even if miners want to continue mining they must prepare and propogate their own forked software. There is no "do nothing" default option.
With this safeguard in place, to change the roadmap, they need to gain support of users at large, by getting them to actively switch to their fork, just as the roadmap supporters need to do.
Therefore, supporters of change and statis are on equal footing, ensuring that the system isn't biased toward stasis even when the roadmap calls for change.
To summarize, the difficulty bomb encodes the roadmap's plan to implement a change in the protocol, into the protocol, graduating the plan from having mere social consensus, which requires active participation to enforce, to having a technical one, which is autonomously enforced.
Hence: the very definition of a fork, that is some blocks seen as valid by some faction and seen as invalid by others.