Please allow me to dance on a few eggs shells here and answer your post with some questions. Do you ever do any portrait work that is not in-studio? How about portrait work that does not involve young women? Would ever consider a shot of an elderly women on a park bench? Perhaps an older man in a barber's chair? How about a bowler who has just made their first strike...that expression of pure joy of doing something they have never done before? I realize getting these types of shots take huge amounts of time and dedication, but that is what makes them so impressive.
To me, studio work lacks authenticity. It screams fabricated, which never piques my interest. I am all about 'the moment' when it comes to impressing me with a shot. I say this out of a desire for those kinds of shots, not because I am involving myself with that kind of shot, so please don't deem me hypocritical.
Perhaps, if you were to post some people shots that were more organic you might get a better response. It would certainly encourage me to post more on your work.
As to why you get better response from other sites I would say that 'different strokes for different folks' might apply here. The demographics of sites varies, and far be it from me to put a finger on why it is that way. Take DPReview for instance. They are primarily a product review site with very little emphasis on posting of shots, while here at TPF we are all about posting shots. This discrepancy will undoubtedly attrack different viewers.
Here's hoping that you take this as heartfelt advice and not malicious, or insulting.