All jokes and "snarkiness" aside, it's just a matter of habit. If the whole world used UTC and working hours/social time were set differently per-country, I bet we'd get used to it eventually.
Now might be a great time to do something like that. It doesn't sound like a serious proposal, but there would be interesting benefits to city-based timezones again in the modern world. We actually have the technology to scale smaller timezones now. We aren't relying on mechanical clocks like the train companies were and paper calendars like early multi-timezone companies like GE were. We could make local time resemble solar time a lot more again, and solve it as a software problem.
The other problem is that I don't think habits would be easy to change. Right now people in some european countries want to stay permanently on summer time to have more daylight after work. We could just as easily stay on winter time and have everyone go to work earlier, shops could open at 7 instead of 8, etc. But for some reason this isn't considered, so I assume it's easier to enact all year DST than to change working hours.
Like should public holidays e.g. start and end right in the middle of the solar day because that's when midnight UTC happens locally? Do you reintroduce time zones by the back door by defining a local start/end time for day-based events to align them back to the solar day?