Plath,
I know how you feel, my mom always had time to watch my niece and go to every game, school event, everything, but when we asked it was like pulling teeth.
I would get so pissed, I was the one who did everything for my parents and my sister and her husband were always a drain, always needed help, always borrowing money, etc.
I could never get an answer from my parents about why this was the case, they pooh-poohed it every time I brought it up, I was imagining things.
IMHO there is not a damn thing you can do with this except drive yourself crazy.
Are there any other moms in your building or nearby, is there a mothers club in the area you could join?
Wish I had some good ideas for you, we just had to adjust to the reality that our parents talked a good game but could not follow through.
It has really cost my parents a relationship with my kids as they have grown up and realized how unimportant they really were.
Hang in there,