The 'career' wage is definitely a factor in retaining instructors, but if, as suggested by GAPAN there is a career instructor rating instroduced where are all the young PPL instructors sourced from? Surely there would be a shortage.
To defend the current non-career instructors, a letter was also posted in either Flyer or Pilot a few months ago from a CFI regarding his current commercially orientated FI's, saying they are the best he has worked with in a long time. At least they have a wider respect for aviation than just C172, PA-28, AA5-A.....