Who gets to pick when “noon” is when the sun is usually above their head? Let’s assume Greenwich for posterity sake. That means a bunch of the world will spend most of their “daytime” in traditionally nighttime hours. Thus spending your day (time when the sun is up) and your day (the time when you do your work) will not intuitively mean the same thing
complicates both secular and religious law
Islam requires regular prayer in the direction of mecca and plenty of nations have Islamic law. At a minimum they’d have to rewrite those laws, at most it’d cause a literal schism
is a staggering inconvenience for a minimum of five billion people
“We changed how clocks work for almost everyone on the planet to make some nerds’ lives easier. Please go change your planners, clocks, schedules, applications, signs, etc to adjust”
makes it near-impossible to reason about time in other parts of the world
In most of the world, you can reasonably assume the sun goes up around 7 am and sets around 7. Obviously that changes but you can pretty reasonably assume when people will be around and doing stuff by looking at their time. In this new system you’ll need to figure out what times people do most of their activities based off of geological segments of the planet and checking what their “daytime” is. Which is already a problem timezones address
is not simpler at all
On a base level maybe, but after fixing all the other problems it causes the resulting system would likely be just as if not more complicated than our current time system