Because the time zones are there to reasonably align with sunrise and sunset. It’s not perfect, but better than being in full darkness in your area at noon GMT.
If the Aussies and Kiwis can celebrate Christmas in the summertime, I don’t see what the problem with “dark noon” could be. That’s what the northern Scandinavians deal with for several months of the year.
I guess the point is that everyone would eventually adjust. “Time” is a man made concept. Whether you work for 7-330 or noon to 8:30 really doesn’t matter. It’s still eight hours.
The military has used “Zulu Time” for a long time now. It tends to coordinate things very nicely.