Not to mention the massive advances of the Industrial Revolution, continuing through the technical advances of the 19th and the first two-thirds of the 20th. Since then things have become pretty lame in the West, which now largely spends its time and money navel gazing, and wondering whether it is being politically correct enough. Which is why China and India are now getting ahead of the West, having no such distractions.
These things are to do with fashion. Currently, "diversity" is in fashion in the West, and whatever is in fashion is likely to attract brighter, younger people. If homogeneity were in fashion, that would attract brighter people. As a historical example, early medieval monasteries, about as homogeneous as communities could get (at the time) attracted the brightest young men. That is because they were in fashion at the time; and even if you did not want actually want to join one, you sponsored one if you were rich enough. The monks wanted to get away from the bustling, hedonistic, "vibrant", "diverse" society outside, which they saw as a world that would not last much longer, and was descending to Hell. Of couse, by the late middle ages many of the monks had become "diverse" and "vibrant" themselves, meaning that they had turned some monasteries into bawdy houses and drinking dens. One reason why Henry VIII could dissolve them.
The fashion for diversity might soon be over however, now that people are beginning to see how it works in practice, especially recently.