Calendars serve for several purposes.
Every calendar has its specific features and applications, its advantages and disadvantages. But it is claimed that the Gregorian Calendar in its modern version fits in the avarage better to all our purposes than its rivals. All time scales used nowadays have a 0 and negative numbers. Let us consider for example the pendulum experiments performed by Galileo. Nobody would even come to the idea to denote this time scale an astronomical second numbering system.