Classic divide and conquer.
I'd expect the main driver would be different groups within the workforce feeling that they're different sorts of people hurting efforts to band together, for which it's mostly subjective diversity that would hurt. The sort of thing where a mix of old-stock Americans, Irish-Americans, and Italian Americans would have considered themselves racially diverse in 1920 but not in the modern day.
Other potential things would be different languages, different notions of fairness, attending different social organizations, etc.
[1] https://en.wikipedia.org/wiki/List_of_ethnic_groups_in_the_U...
Thucydides noted: "A crowd like that are hardly likely to respond unanimously to any proposal or to organize themselves for joint action"
I've also read the "conspiracy theory" that racial division is pushed in an attempt to disrupt solidarity based on economic class.
Hardly a conspiracy theory when it is on record during the Civil War and the Southern Strategy.
https://www.bls.gov/regions/southwest/images/36642.png
https://www.uky.edu/Projects/TDA/BlackKentucky/maps/percent_...