timelets

Labor markets in U.S. cities today are vastly more educated and skill-intensive than they were
five decades ago. Yet, urban non-college workers perform substantially less skilled work than
decades earlier, and the once robust non-college urban wage premium has largely flat-lined.
....

The urban workforce is disproportionately college-educated and foreign-born, and it has become more so over time.

[T]he second differentiating feature of urban labor markets alluded to above: the rise in immigrant intensity.. In 2015, the rural-urban gap in the foreign-born share of college adults was approximately 35 percentage points, roughly twice as large as in 1970. Similarly, the rural-urban gap in the foreign-born share of non-college adults was approximately 25 percentage points in 2015, again roughly double the gap in 1970. Foreign born workers in turn have a bimodal education distribution: they are disproportionately likely to either have completed post-baccalaureate education or to lack a high school diploma.

https://economics.mit.edu/files/16724

Also see the developments in online marketplaces, which make non-college services work standardized and replaceable. https://a16z.com/2019/01/08/marketplace-startups-then-now/

and here https://www.bloomberg.com/news/articles/2019-02-26/japan-has-a-new-guest-worker-program-just-don-t-call-it-an-immigration-policy