I think you're right in so far that the US never really wanted to do what it would take to convert the whole of Afghanistan to a friendly state, like say Japan

I think you're right in so far that the US never really wanted to do what it would take to convert the whole of Afghanistan to a friendly state, like say Japan after WWII. Urbanization statistics for Afghanistan place them at something like 20-25% with most of the population being rural. So even if you occupy the cities and stay for a generation (19.9 year according to https://www.cia.gov/the-world-factbook/field/mothers-mean-age-at-first-birth/ https://www.cia.gov/the-world-factbook/field/mothers-mean-ag...), you haven't really won the war. The first source I found says that in 2017 about 50% of the population was still under Taliban control or where Taliban openly moved about.