I don’t know the exact history, but the rest of the metric system is designed with a base unit and decimal derivatives. Assuming we want to keep the day length consistent (I can’t imagine a system being practically useful otherwise), we’d have decidays, centidays, etc. and not have hours, minutes, and seconds in the system at all. A system with days, decidays (2.4 hours), millidays (1.44 minutes), and microdays (0.0864 seconds) doesn’t seem bad to me at all, I’m sure people would come up with a good name for 10 microdays for daily use (0.864 seconds).