I suspect most of those instructors whom refuse to instruct in 150's and 152's have never
flown a 150 or 152!

The majority of young instructors nowadays trained in plastic pigs!
Actually, one of the instructors is a fat guy (and getting fatter all the time), and another one is an older guy with bad knees who says the cramped legroom hurts too much since he needs to keep his feet off of the pedals. They both have MANY hours instructing in C150/152's.
The old guy does make an exeption for me, and still agrees to go up for biannuals and such.
Let's face it. 150s/152's are a bit challenged in the interior space and power departments with two grown guys. A 172 is a lot more roomy, comfortable and has more power.