It's not just that they may hit you from behind. That is one possibility, certainly, but by no means the only one.

Drivers coming around a blind curve on a narrow, shoulderless, curvy, hilly road suddenly encountering a cyclist in their path may also:
- swerve into on-coming traffic (I have seen this)
- try to jam you into the right or push you off the road entirely (I was warned that this happened to someone on a road I use)
- sideswipe you
- slam on brakes, become road raged and then who knows what
- handle the situation fine but wait for you at the next stop to give you a lecture (I've had this happen)

I regularly share these types of roads with large SUVs and large work trucks (people who work in construction or related fields like gardening and plumbing.) A lot of these people are in a hurry.