I'm a 5'9" guy who is actually shorter than that as I shrink with age, which is a thing for those younger among us.
The world is built for, and has been for a long time, average-sized people, which means that being 5'8"-5'10" (for men) means that proportions of doorways, car seats, commercial aircraft, theater seats, bed mattresses, clothing, ALL THINGS built for people to actually use, are made for them.
Not only that, but average height people tend to experience fewer lower back problems, something that not-infrequently means chronic suffering as we age.
Ease and comfort for traveling, ease of use with vehicles, never needing to worry about feet hanging off of the mattress, ease of finding clothes that fit well, ceilings and doorway proportions all good, few worries about breaking down physically due to lower back issues with age, the perfect size for the average size woman, not having to worry about nasty shallow/vain women for whom height is the important thing, I could go on and on.
In the end, in a world proportioned from a practical sense for the average human form, it's pretty great being average-size.