My paternal grandmother's the same way, all about her husband's grandchildren rather than her own. I can count the number of times I've seen her in the last decade or so on one hand.
i really shouldn't complain because i mean she lives with us, so i definitely get to see her plenty. but sometimes (like all older people) she'll fixate on something, and all she'll ask about is has this stepchild called, have they written, i want to send her a letter.