Why?
Why is the R22 so popular?
...in a word - rentability!
Most rotorheads don't own - they rent. Ever tried renting anything other than an R22/R44?
That said, the R22 is a great trainer, especially given the darn thing was never designed for the role. Master the R22 and you can fly anything. I know...I did it, and almost competently on a few occassions.
Dantruck