How Can My Ex Forget He Has A Daughter?

Today of all days, I just seem to be feeling some anger. It has been many, many months since my ex has come to see our daughter. Our daughter is a very beautiful teenager. Her and I were talking this morning on the way home from the barn and her English riding lesson and I got a phone call from a relative and he and I were discussing the fact that his new partner got mad at him for calling up his ex to see what kind of medicine their son was on because he was coughing so much. I was livid!!! Every father has a right to call the ex to see about their child. That child doesn't have just ONE parent..... which lead my daughter to ask me about her father and why he doesn't call about her, or even come over. I had to explain to her that since her dad is self employed, he has weird working hours and sometimes doesn't have alot of extra time, but that he is welcome to call at any time he wants to see how she is, and he is also welcome to come over to my house to see her at ANY time. Heck, he is even allowed to take her out when he has time at any time on any day !!! I have removed the barrier of certain weekends or whatever so that I can accomidate him because I know how important it is for a father to have communication and visitation with their child. I felt so upset that she is without her dad. He and I still speak occasionally, and we get alone just fine, but somehow, some way, he has totally forgotten about her. He doesn't call. He doesn't come over. How can my ex forget that he has such a wonderful daughter? I honestly do not understand!!