Medical professionals are people. As such, they are prone to the same things as the rest of us. No small number of psychologists went into the profession to cure themselves; some of them have BPD (look for some podcasts on iTunes - some are hosted by psychologists suffering from BPD).
While it is true that professionals are reluctant in diagnosing patients with BPD, compassion or apparent lack of it has not much to do with that. Professionals realize that BPD is difficult to treat as it requires extensive training, time, patience and possible reliving of and involvement with similar things that brought us to this forum. If you go listen to the podcasts, you will hear professionals with horror stories - BPD patients calling their office with threats of harming themselves... . Then getting into severe devaluation of their therapists... . It sounds almost equivalent to what people here are/were experiencing - the whole idealization/devaluation circle along with manipulative behaviors. So, even professionals are not immune to that.
Unfortunately, some professionals are simply not up to the challenge of treating BPD. That is no wonder, it is very difficult to create an emotional connection (it is needed for healing) with someone whose emotions range from severely disregulated to having an "on-off" switch on them. I wish I was just being ironic - that is something that therapists face every day.
Last, but not least, few therapists can truly empathize with their patients. According to Carl Jung, probably the most important and influential psychiatrist to have ever lived, it is crucial for healing that a psychiatrist is able to fully empathize with their patient, and relieve himself/herself of any judgments until the patient is fully cured. He was talking about a relationship where the psychiatrist would be a partner in patient's recovery. It is quite possible that he has not had BPD in mind when he talked about this, but it seems to me that BPD cannot be cured without true compassion. If you are curious to hear what Jung said, here it is:
www.youtube.com/watch?v=jG5fshTs4mQ (Carl Jung on Accepting the Darkness of Self and Others)
The particular statement that I am talking about is at around 4th minute in the video, but I highly advise you listen to the whole thing. Jung is one of the most brilliant minds to have ever been born. And we can learn A LOT from him as to how to position ourselves in the aftermath of our relationships pwBPD. As the name of the video suggests, we have darkness and they have darkness. We have to accept both. We have the advantage over being sound enough to work through it and accept it. PwBPD unfortunately cannot do that on their own. Hence, compassion is the key!