We would invent them for the same reason they were invented for the first time. I don't really care what time it is in England; I care about the local solar ti

We would invent them for the same reason they were invented for the first time. I don't really care what time it is in England; I care about the local solar time where I live. I live in Tucson; the local solar time at my house is about 7.4 hours before UTC. I and the people who live near me would quickly start informally referring to times based on the position of the sun: "let's get lunch tomorrow an hour after solar midday". (Aside: this isn't just hypothetical. It has happened in the real world. In the far west of China, people have settled on a different time zone for colloquial everyday use, which differs from the Beijing-imposed official standard time by two hours.) So far so good, but someone on the far east end of Tucson is more than a minute later than me; if we want to be precise, we'll need one standard for the whole city, so maybe they'd build a big sundial at the University of Arizona and that would serve as the reference for the whole city. But people drive around Arizona a fair amount; it'd be annoying to have to adjust my model of time by five minutes every time I go to Phoenix, and I wouldn't mind the few minutes of slop applied to my own life in Tucson, so I'd probably just start referring to everything in terms of offset from "Phoenix midday" and "Phoenix midnight" to make things easier. And if we're going that far, we might as well make it an even bigger area: big enough to include the whole Southwest, but small enough that the difference from local time doesn't bother anyone. Let's say we base it on Denver. Bam, we just reinvented Mountain Standard Time. Well, almost. Meanwhile, people on the East Coast would have (almost) reinvented Eastern Standard Time, presumably based on their most important city, which is New York. New York is about 1h55 ahead of Denver in solar time. Dealing with these almost-but-not-quite hour offsets would be annoying, so we'd probably just standardize on one system for the whole country, with nice, even, easy to reckon hour-multiple offsets for everyone. Canada and Mexico, whose economies are highly dependent on trade with the US, would soon standardize on the US-imposed time zones. Even if doing so might hurt their patriotic sense of national pride, the practical value would be too great. But what about the rest of the world? Well, our historical closest friend and ally in a far-off longitude is the UK, so why not sync up with them and make all those easy to reckon hour-multiple offsets from their most important city, London, or more precisely, the point they've chosen for London's standard time: the Royal Observatory in Greenwich. Now we really have reinvented Mountain Standard Time, exactly as it exists in the real world. Why wouldn't we go further and just use Greenwich time for everything? Well, because we still do care about local solar time. The difference from my house's solar time to the newly invented MST is less than an hour, which I can live with, but dealing with a 7-hour difference would be annoying.