I think that's a valid argument to be made. Stats have shown the Republican party has become more blue collar over time [1] and that white collar workers are trending left over time [2]. This would explain why the gap is growing: blue collar workers make less and sacrifice more of their health on the job than white collar workers. Blue collar workers also generally don't live in cities, because factories and industry aren't located in cities.

[1] https://www.nbcnews.com/politics/meet-the-press/gop-rapidly-...

[2] https://www.washingtonpost.com/politics/2022/01/11/democrat-...