This coordination breakdown happens because a shared calendar is a static view of time, whereas a service business is a dynamic operation. A calendar doesn't understand the geographic logic of a route, it doesn't know the specific skill sets of your staff, and it certainly doesn't alert you when a morning job overruns, creating a ripple effect for the rest of the day.
The core problem is that a calendar is a "disconnected tool." It doesn't talk to your job records, your asset list, or your team's live location. When you have 5 staff, you can manage these connections in your head. When you have 20 or 50, the manual effort required to keep the calendar "true" becomes an admin bottleneck. You are forced to become the human bridge between the schedule and the reality of the site, and eventually, that bridge starts to crack.