I’m sure this will be a hated post but here goes. Since the woman manages and plans most things in a family, the default is nearly always tipped towards her parents and siblings. It plays out that way in nearly every family I am close enough to know about.
So, if you’re the mom of boys, think hard about how welcome you make your in-laws feel. You’re creating a blueprint for your own kids. I have all boys and I realized what was happening early and made a conscious effort to overcome, with mixed success. I wasn’t good at all with spontaneous stuff with my in-laws. Now the shoes on the other foot. They all try but they live far away (of course near the in-laws). Men need to step up their involvement in family events and women need to recognize this pattern.