Edit: Today I learned that UTC is an actual real thing and not just a setting I scroll past on my computer 😅.
They also complicate things.
It made more sense back before we had electric lighting and when everyone lived by the rising and setting of the sun. Now it doesn’t seem to really matter.
Obviously, the whole world deciding where to start the time would be nigh impossible but it could be like: starting at this date, on the first day of the year, what ever point is farthest away from the sun is 00:00 from henceforth.
And then people just adapted to what that meant for their particular area. Somebody’s morning might be 13:00!
Imagine if the whole world was on some global time schedule.
Edit: From my comment below
Look at the earth from a top down perspective. It’s a pie. With 12 or 24 slices depending on the granularity. A clock, basically. It would take the same amount of energy to learn which slice of earth is lined up towards the sun for each hour as would be to learn anything else in elementary school.
After which, for the rest of your life you’d have an intuitive grasp of where earth is in its rotation and what “time” it would be for any place in the world.
As someone who travels quite a bit, that would be hellish.
It provides a consistent reference for information sharing. E.g. you move to a new area of the world. Assuming a 9-5 work time is a reasonable baseline. Assuming a kids bedtime is 8pm is also reasonable, etc. Without timezones, you would have to relearn all of those.
You would also be required to memorise those details for friends and relatives who live abroad. E.g. if a friend moved from the UK to new Zealand, you just need to memorise the time offset. That way it becomes easier to catch them before work, or before bed, rather than in the middle of work, or while they are asleep.
Ultimately, both in parallel is likely the best option. Local time for local events, UTC for global level events or referencing.