I guess I’ve become the 12hr clock simp here (I’m not tho, use whatever) so here I go.

Forget the minute hand. If I have a 24hr clock, the hours will be more crowded. Meaning that the per-hour angle of each number is halved. I’d imagine this somewhat limits clock design or runs the danger of being harder to tell which hour you’re actually on with a short hour hand. The numbers must be smaller and the hour hand must be longer for the same accuracy.

And yes you are losing technical accuracy with a 12hr clock. But a few things about this. Again it’s more about that humans actually experience time in smaller segments than 24 hours. You don’t experience a full 24hr day. You usually experience a smaller segment like 12-16 hours. This is especially true if you divide your time into day/night or work/leisure.

Now the obvious downside like you mentioned is the am/pm thing. However, that usually isn’t a problem and I don’t get how people would reference 24hr clocks in conversation. Do they say “yeah sure, we can grab drinks at eighteen hundred” or “eighteenth hour” or do they just say eighteen? (American problems).

It’s usually not a problem because context goes a very long way. If I ask you to grab lunch at 2, obviously it’s 2pm. If I ask to grab drinks at 8:30, it’s pm. Most social events come with a time context and most social events are in the afternoon. There’s surprisingly little overlap between events that would be early morning/late evening.

And yes I know digital clocks the formats matter less. It’s a preference thing, no one should care much.

As for the reason for 12 being the changeover time, it’s all for analog clocks. Looking at an analog clock, when determining the hour you draw a line out from the hour hand. Whatever is the nearest number counter-clockwise, that’s what hour it is. So the 12th hour exists. Otherwise you’d have it go from 11:59 to 0. And zero o’clock makes no sense, especially at noon. Again, no clue how anyone would reference this in 24hr. Half passed midnight maybe? But again if you can say pick me up from the party at 12:30am, you don’t have to reference midnight but people still do sometimes.

As for 12am vs pm, it’s simply because the clock transitions at its apex. If it didn’t, it’d be confusing. Also 11:59 is midnight in either system, so it’s the middle of the night. And it creates an obvious transition for midday to exist.

I hope that clears up why the system exists and why I personally prefer it. Again, use whatever works, but I promise the system works pretty well for everyone that uses it. The more disruptive thing is daylight savings time, not the system itself.