It's a whole lot easier when your friends have kids. Otherwise you get left behind.
In the past, lets say baby boom years, almost everyone had kids so the family friction coefficient was very similar between different friends.
But these days it's quite different. We typically don't leave our kids at home alone any more (GenX represent!). There is also a much larger group of people without kinds (DINKs and SINKs) that have far more free time than those with kids. So for them the equation changes.
They have the cost of inviting you and the friction you experience. Or the cost of inviting the childless friends they know. Or the cost of the myriad of entertainment options we have these days.