Calendar sharing is a solved problem technically and an unsolved one practically. Two adults share calendars, and within two weeks one of them has turned the other's off. The reason is almost always the same: the shared view is unreadable.
A wall of everything is a wall of nothing
Work calendars are dense. Overlay two of them plus school dates plus a practice schedule and Tuesday becomes a solid block of color. The information you actually needed — who is picking up the kids — is in there somewhere, competing with a recurring stand-up.
So a household calendar has to be selective by default. It shows household events. Work stays in work's calendar and appears, if at all, as a busy band rather than a title.
The other half is writing
The second failure is that adding an event to a shared calendar is a chore. If it takes six taps and a decision about which calendar it lands in, people stop doing it and go back to telling each other. An event that took a phone call to arrange should take one line to record.
A shared calendar earns its place the week it answers a question nobody had to ask out loud.