> Despite its prominence, for over 20 years almost nobody has used this approach. Why is that?

There is one highly successful use of REST: the World Wide Web.

The Web/Web browsers are driven from hypermedia. (This is circular, as Fielding was looking at the web when making his dissertation.)

Granted, Web browsers stand alone as an application with extreme flexibility.

So REST is both highly common and very rare, depending on how you count.