because we sleep at night and are active during the day, and so we need to track that in a way that is universal. if i mention 12:00, people understand that it is noon where i am, and if i mention 22:00, they know it's bedtime.
the whole point of time zones is to have time cohesion in a wider region within margin of error, so people on the far east and far west of a time zone are close enough to solar noon at 12:00. you can take a train to a neighbouring city without having to worry about needing to adjust your timekeeping devices by a few minutes.
to put your scenario into perspective, china has already done what you suggested on a smaller scale: the entire country is on UTC+8 for the sake of "unity" and "national cohesion". beijing loves it; 12:00 is still noon there! except it ain't in xinjiang and tibet. xinjiang has its own unofficial xinjiang time zone of UTC+6, and so people have to specify which time zone they're talking about and convert times between the two time zones in conversation because the uyghers use xinjiang time and the han chinese use beijing time, and you can imagine the confusion and also technical issues that has arisen from that.
imagine that, but 12 times worse. no thanks, i'll do the simple math of converting time zones if i ever need to communicate internationally.
fuck daylight savings. take that shit out back.