For global communication, it helps to form a mental model of the other side. When you pick up the phone to call someone else, knowing it's 1am there would typically indicate you should likely think twice before calling.
It's a crutch to enable a more convenient mental model for most people to relate to what time of day it is 'over there'. Otherwise, sure, there's no real point.
right, but I never know what time it is there. I only know what time it is here. And maybe I have a relative sense that there is 6 hours east of here. Often I don't even know where it is I'm talking to. I called the help desk, I have no idea what continent picked up the phone.
"office hours are 22-6 UTC" would be much simpler than "office hours are 9-5 EST. hmm ...is that european standard time, or east coast of the usa?"
That's a good argument in favor of keeping time zones, but it's not why we have them.
The reason we have time zones is because people started keeping time long before fast travel and communication made it necessary to consider what time it was on the other side of the mountain, let alone the world. The reason we keep them is because the status quo is hard to change.
It's a crutch to enable a more convenient mental model for most people to relate to what time of day it is 'over there'. Otherwise, sure, there's no real point.