My T does not acknowledge holidays in that way either. Well, he might do an exception for Christmas but this is an exception - I have had therapy session on my birthday and I have said that it is my birthday (just as part of saying anything that comes to my mind) and he has never wished me happy birthday.

For me it is somehow logical. If he would acknowledge the holidays then he would somehow force his views about those holidays on me. I am in psychoanalysis and there just isn't basically any room for polite chit-chat. I don't feel bad about it because it would feel like a burden to me. We are very close emotionally and I can talk to him about anything, so if his not wishing happy holidays would bother me we would just talk about it to understand why I would want it from him and by doing that I could learn something important about myself. If he would offer those wishes by default then the road for such discussions would be blocked.

So, my guess is that when a T does not acknowledge holidays it is because he/she wants to give you the opportunity to discover anything that could surface from that. I personally think that having opportunities of such discoveries are more important in the context of therapy than following the common social rules.

I guess you never talked about those things with your T during your 6 years with him. One option would be to go back and talk about it to see what lurks behind it.