Guy, it probably happens to ALL of us and not necessarily because of age either.  As Anik has suggested, something ELSE is going on.  After all, the gal DOES know you because she has seen you once.  For whatever reason, apparently she does not choose to again.  It could be bad chemistry or something that you said or did (or did not do).  As a much older guy, I can tell you that you just NEVER know with women.  You would if they would just TELL you, but my whole life I have experienced that they hardly ever do.  Somehow you are supposed to just know what it is or figure it out for yourself.  You're also supposed to just get the fact that you are being given "the brush".  Well, join the club.  I have found that the hobby is no different in this regard than real life.  

 A couple of things to consider.  You can avoid all this by resolving that you are going to try to see a different provider each time.  Yes, they do communicate with each other.  Yes, you do need references so hopefully this doesn't happen early in your hobbying career.  Whatever is up with her may be just her, and it may not affect your reference (though you can't count on that).  

 I can tell you that I prefer solid regulars, as well.  However, bear in mind that this does not make one immune to "the brush".  I have certain women who I have seen perhaps a dozen times or more become impossible to get.  Some of such gals may be doing it BECAUSE it IS the hobby and they do not want you to get too close.  If you are lucky, you may have one or two that you can stay with for years.  If you find that you prefer regulars rather than a lot of "notches on your bedpost", realize that you will occasionally lose one or two and that you will have to get out of your "comfort zone" and go out there and replace them.  Realize that may not happen overnight.

 I agree with you that it is "SO SADD" that people cannot or will not communicate.  We are not telepathic.  We HAVE to talk to each other.  However, realize that the gals have a considerable "numbers advantage" over the guys.  When you think about it, that is why there IS a hobby in the first place.  When people have a lot of choices, it can be very easy for it all to "go to their head".  This can be especially true with younger providers.  Something else to realize when you might otherwise want to dismiss a gal over 30 yourself.  Frankly, I tend to prefer the more middle aged gals and their maturity.