The reason I don't believe in it is because in my opinion, a client does not know the therapist as a real person. The person the therapist truly is can only be a stranger to the client. So to me, if one was to think they loved the the therapist they hired - it would be that they loved a fiction - the therapist persona played by that person hired for that appointment period of time.
And I don't think most therapists feel love for clients. They may like or dislike the client, but I don't the client matters enough to most therapists for the therapist to feel love towards any specific client.