Additive Manufacturing, industrial robotics, the Internet, and the proliferation of computers had already made large portions of manufacturing and low skill white collar jobs redundant by the mid-2010s.
Furthermore, the brutal reality is most businesses can generate revenue growth just by concentrating on the 90th percentile and above of households [0], (edit: or at best the 70th percentile of households of income [1]).
For example, despite all the love Costco gets on HN - the reality is it only targets customers within the top 50% of households by income [2]. You may delude yourself into thinking that you are a thrifty underdog when you shop at Costco, but the reality is most Americans cannot and will never be able to afford Costco, and Costco doesn't want or need their business.
A K-Shape Economy is actually the historical norm.
[0] - https://ourworldindata.org/grapher/income-share-of-the-top-1...
[1] - https://dqydj.com/household-income-percentile-calculator/
[2] - https://www.businessinsider.com/how-costco-sams-club-shopper...