"We're collecting money for so-and-so's new baby"

I don't mind chipping in money for a co-worker's new baby. I've been doing it for years. I do it knowing that when I have a baby, they would do the same for me. Well, I had a baby and some people that I've contributed to, did not return the favor. This is not one of those situations where you're giving them a gift like Christmas or birthdays and you don't expect a gift in return. I am contributing to help out a set of parents get started because a baby has a HUGE start up cost. So you would think that they wouls realize that and help me out. Some people just doesn't know how to be a good co-worker. Ugh.