I’ve had instructors that were simply content with teaching PPL maneuvers in the same practice area to build their time, and others that sought to vary their teaching and aviation experience by becoming a CFII, MEI, spin instructor, etc.
If I were to ask my first instructor if he plateaued, he’d say definitely and should have been at an airline hundreds of hours ago.
The same question asked to the latter pilot (my last instructor), he’d say no way as he still has much to learn. I imagine most here have flown with both types of instructors at some point in their career.
Not saying the first instructor is necessarily in the wrong, as I recognize additional instructing opportunities are not available everywhere, but some treat instructing simply as a means to an end and others treat it as their profession.