I'm not sure how to think about what you mean by "almost never." If most commercial software is web frontend + monolithic app code + relational DB, then you may very well be right.

That doesn't quite match my professional experience, though - there are so many companies building databases, message queues, filesystems, and similar infrastructure. Sometimes they're internal projects, and sometimes they're commercial products. I've always felt that those systems would benefit from formal methods, since they're usually trying to provide strong guarantees to the application code on top.