It doesn't help under normal operating conditions. It takes roughly 16ms at the speed of light to cross the US. 16ms is also coincidentally one entire cycle a

It doesn't help under normal operating conditions. It takes roughly 16ms at the speed of light to cross the US. 16ms is also coincidentally one entire cycle at 60Hz. So, who should sync to GPS and at what phase? In addition, when the grid begins to get overdrawn, the phase begins to slide due to the physical nature of generators. Global sync doesn't really matter; local sync is what's important.