I think this kind of thing happens far too often (really, even once is too many for the clients on the receiving end), but I don't think it happens in most cases (but that is no consolation if you were the case where it did happen).

I have never been dumped by a therapist, nor have I felt abandoned. I have had therapy have to end with two therapists because either they or I moved, but I never considered that at all abandonment. My therapists never promised they would be there for me forever, nor would I have ever expected them to be -- that's unrealistic. They did say they would be supportive and work with me so long as our work took, barring obvious circumstances such as job moves, retirement, death (honestly, they didn't have to say that; those kinds of circumstances seem obviously apparent to me in all things).