It's all very well making grandiose comments about instructing for instructing's sake, but the reality is it clearly does not pay the bills. Most instructors I have met are having to work other jobs just to survive. Maybe that's ok for a while, but I don't think it's unreasonable that people should want to see a future beyond instructing before going down that route.
I would also say that I did my ppl over a few years at Cabair, and therefore had a number of hour building instructors, all of whom were excellent. I think personality is the most important factor. You will get some hour builders who have a natural flair for instructing and are brilliant, and some "career instructors" who are crap!