The friend on the fringe

I have lots of friend groups that I'm on the fringe of. This means that these folks are more like acquaintances than friends. I get invited along when it's convenient in some way, but these are not people I could count on in any way. Like to me, real friends show up with a bowl of soup if you're sick or you talk about things you're going through and provide each other support. I can feel it when I'm being pushed to the fringe. It doesn't seem to matter what I do. I am just wondering why this is, and if there's anything I can do to change it because it is super lonely?