It's not used more because it is unknown, not because it is difficult to use or that it is impractical.

I've written several libraries and several services now that have 100% coverage via CBMC. I'm quite experienced with C development and with secure development, and reaching this point always finds a handful of potentially exploitable errors I would have missed. The development overhead of reaching this point is about the same as the overhead of getting to 80% unit test coverage using traditional test automation.