Are you sure no one is spraying the roadside to keep weeds down and reduce mowing? Bermuda will usually grow anywhere - I've seen it come up through concrete and asphalt pavement.

No, we live in a small subdivision where everyone seems to love their weeds. There's only about 4 homes in the neighborhood that seems to care about their yard. Most people only mow about every 3 weeks. Drvies me crazy. I did get me some fast acting lime yesterday. I got up all the rock I could, added more fresh dirt, the lime, bermuda seed and barely covered with a very light layer of mulch. Watered very well. We'll see what happens.

You could also just put a layer of mulch down on the bare soil. As the mulch breaks down the bermuda will move in and grow through it. You may have to re-mulch every year for a while until the grass really covers the space.