I think we need to remember. . . that a lot of energy was put into changing things to get us to the point where we are now. But being where we are now doesn't mean that we don't have to put in the same kind of energy to get us to a place where we ought to be.
There's a sort of sibling moratorium when you're establishing yourself as an adult. So much of your energy has to be focused on other things like work and kids. But when people become more settled, siblings tend to regroup because now you're building a new extended family.