https://en.m.wikipedia.org/wiki/Swatch_Internet_Time
Time zones exist so that (approximately) the sun is overhead at noon. If you ask anyone what time zone the world should operate on, they’ll agree, provided that they use your time zone. Otherwise you could make everyone use GMT/UTC instead, and I can’t see America doing that when most of the country can’t count beyond 12 on a clock.
There are some counties which use a single time zone by dictat, like China, but all that happens is people adjust their working days such that the sun is up at lunchtime, so you don’t gain any advantages by having everyone on the same time zone because now you need to know what individual areas working hours are so you can communicate.
These days more problems are caused by leap seconds, which is the difference between GMT and UTC, and I expect we will get rid of those soon as well.
As a result it is easier to abolish leap seconds and just live with the fact that in 30,000 years time that noon might not be directly overhead.
I'd actually be curious to hear what a nation wide timezone would solve?