I don't see what makes the second less tied to the Earth than the day. The SI system is for scientific purposes, it doesn't have units important for civil purpo

I don't see what makes the second less tied to the Earth than the day. The SI system is for scientific purposes, it doesn't have units important for civil purposes like liters. If you were to completely redefine civil timekeeping (good luck!), the day feels like a better unit to focus on.