Because then you'd still need an almanac of the drift in determining celestial location/navigation. It's easier to just keep high noon at the Greenwich observa

Because then you'd still need an almanac of the drift in determining celestial location/navigation. It's easier to just keep high noon at the Greenwich observatory as the defining datum, since most worldwide coordinates ultimately reference back to it, being 0deg longitude. Ultimately, either time or location would need to be adjusted, and it's easier to do time. Plus it's consistent with what's been done historically.