My belief is that part of the reason state machines are not used often is: - State machine libraries are good at expressing an existing state machine but often

My belief is that part of the reason state machines are not used often is: - State machine libraries are good at expressing an existing state machine but often the workflow for upgrading or modifying it in production is lacking. If you want to remove a state for instance, it's still very hard and the tooling just makes it more obtuse. - The reason class hierarchies as a way to model your problem are overused in most programming languages is not because it's good, but because it's a language feature that's taught by every book that covers that language. If state machines had language-level support/keywords, more people would use them. (Interestingly, I think part of why class hierarchies can be a trap is similar to the first issue above with state machines: they are hard to change down the road as you learn more about your problem space.)