One solution is to plan less, and to get comfortable with the stigma of unplanned meet ups—which is currently characterized as “lazy and non-committal.” They’re also less ambiguous; the lack of definition—and the accompanying freedom—is also part of the appeal.
As life moves forward, with more people taking on greater commitments, jumbled schedules seem like an inevitable outcome. Even if you don’t want it, your friends will practically force you into it. However, there’s a way to approach scheduling with a sense of controlled sloppiness—mixing your schedule with spontaneity—you start to perpetuate spontaneity as well. You can make rules like keeping your Sundays free of plans, and maybe other people will copy you. Or you ask some of your friends to see if they’re open to you calling them and chatting briefly, just for several minutes.