Yet again why the arbitrary limitation? Your own source shows about a dozen areas going from the 5-8 band to the over-8 band since 1990. More than two dozen going from the 4-5 band or lower to the 5-8 band. When each multiple represents most of $100K. When the entire graph should ideally remain about the same color overall but is clearly getting worse. Buy hey, let's look only at the top 10 out of 392 and ignore the fifth of the population that's not in an MSA. That's totally the way to "systematically isolate root causes" ... so long as the root causes are the ones we find convenient. Otherwise not.
In the top 20 most populous MSAs, only 7 experienced a substantial multiplier increase.
In the top 50, it's even less.
The further down the list you go, the less likely there has been a dramatic increase in home-price-to-income ratio.
There's a whole collection of "Fine, American cities" (https://twitter.com/jmhorp/status/1221828340656431105) where multipliers have either not increased, or decreased.
There aren't "hundreds" of places. Here's a list of metropolitan statistical areas (MSAs) by population -> https://en.wikipedia.org/wiki/List_of_metropolitan_statistic...
In the top 10, only 3 have experienced a dramatic increase in income-to-home-price multiple -> https://www.jchs.harvard.edu/home-price-income-ratios
Of those that have experienced a dramatic increase, the root causes are common: restrictive land use policy that prevents us from building more housing. One may call that "tunnel vision", but others may call that "systematically isolating root causes".