Probably has to do with hardware and firmware roots. Building an RTC that is programmable with year, month, day, hour, minute, second without multiplication and

Probably has to do with hardware and firmware roots. Building an RTC that is programmable with year, month, day, hour, minute, second without multiplication and division is much much easier if you store the date time in year, month, day, hour, minute, second. You just need some simple comparisons whenever there is a rollover.