Why is solar position so important compared to ability to coordinate simultaneous events across wide geographies? It would be much simpler to have a globally consistent definition of time/simultaneity and treat other things (like solar position, working hours, etc) as scheduling constraints.

We put up with crazy things in an attempt to match solar position. The meaning of time we all use is flawed when I can hop on a plane and go back to yesterday. That's quite inconsistent with the accepted definition of time as unidirectional.