Everything hinges on our rotation around the sun - at the most fundamental level: seasons, crops, construction schedules, even military campaigns. From there on

Everything hinges on our rotation around the sun - at the most fundamental level: seasons, crops, construction schedules, even military campaigns. From there on up we get holidays, sport seasons, business cycles. These things have to match up to the calendar from one year to the next or there will be chaos. If our calendar is off by a second or two a year, it's very easy to correct without confusing the general populace - most people want to spend precisely zero time thinking about calendars and orbits. Currently, only a few nerds have to worry about leap seconds and the like. And it's part of their jobs, so it's OK. In a two-calendar system, every human will have to keep track of a personal calendar and a scientific calendar. Asking people who don't care to do that - and to fix an issue we already have an almost zero-friction fix for - is a non-starter.