Explaining Why Dad Doesn't Come

I see the look in my daughter's eye tonite as we go out to a fiesta, and she's supposed to be smiling and happy, but she's sitting there with tears rolling down her cheek. I ask her what's wrong and she turns to me and says " mom, I miss my dad". Oh, I really feel bad when she says that, because I know that there is NOTHING I can do about it. Of course, I try and explain to her that even though he doesn't come, he still loves her, but maybe he's just busy. I have repeatedly tried over and over to explain to her dad that she really needs to hear from him, at least on some type of a normal basis, but it just seems to go in one ear and out the other. What's a parent to do in this case? How do you explain to your child that her dad doesn't come to see her because he just doesn't make the time to do so? I don't understand, and neither does she. I cannot tell her anything bad about him, because I am just not that way. I want her to know her dad as he is, with all of his good traits and with his bad, but she needs to find those things out on her own. Why can't he just make a little bit of time for her? It's beyond me why he has to be this way.