I personally have never really felt the shortage of either quantity or quality. Rates have gone up, that's for sure. When I started in Jul 2014, the common rate was 200-250. Now it ranges 250 (if you are lucky) - 300. This hobby isn't really cheap.
I am sure many of good SP's have left but I think that is just the nature of this profession. Girls start doing it till they have enough funds to go to school or college or whatever else they choose to do. Many a time we notice it only when one of our favorite go to gal leaves. Having said that, there are few ladies who are still active for a very long time.
PS: Just saw my dear friend Herb Elly's post. I totally concur with him.
T8E