> Why can't they, for instance, simply declare that school/offices open at 10am instead of 9am for six designated months every year instead of imposing this adjustment on the entire world.

For what it's worth, I've (British) never understood that either. Need more daylight hours for farmers to work or whatever, sure, no problem. But.. that's easily resolved as you described? And before widespread centralised time and access to it, surely they just started at sunrise or soon after, whenever the sun happened to rise. I don't get it.