How uncommon is it for foster parents to stay connected after reunification?

I fostered some children years ago and after they went home I have stayed in contact. I see the kids about once a month and have helped out the family here and there. Recently, the children were placed back into care. Unfortunately, not with me as the parents had more children and I am simply not equipped at the moment to take everyone in. I've talked to the caseworker and other folks from CPS and they all look at me like I'm some kind of unicorn. They can hardly believe that I'm so close to the family.

I get that it is a strange situation. I have been able to maintain a friendly relationship with their mother and when they went home I took a break from fostering and then decided not to do it again so I have more freedom to help them out. It just feels weird that more families don't stay in contact to one degree or another. I don't expect it to be super common, but I wouldn't expect it to be as shocking as it seems to be.

Has anyone else been able to maintain contact with children they've fostered in the past? Why or why not? How has it gone?