"Multiple media outlets point out that the COVID-19 pandemic prompted residents in expensive metros to relocate to a state like Florida boasting tax benefits, lower costs of living, and warmer weather (at least relative to the Northeast)," the analysis by Victor Calanog, Lu Chen and Xiaodi Li notes. "While these newcomers bring additional business to the local economy, they also stiffened competition for housing and likely bid up multifamily costs, thus intensifying the affordability predicament."

Meanwhile, multifamily rent burdens actually decreased in so-called expensive metros in 2020—think cities like New York, San Francisco, and Washington, DC. But "this brief respite did not last," the Moody's analysis notes: rent-to-income ratios increased more than 30% by Q4 of 2021 for expensive metros. But while expensive metros typically have higher incomes to match, Moody's points out that median household incomes tend to be lower in inflationary metros. And "if multifamily rents rise faster in lower-income areas, poorer households bear a proportionately larger brunt of the rent increases brought about by these trends," the trio note.

The crisis bears out in single-family homes as well, with prices rising by 54% in inflationary metro over the last five years, outpacing the growth in expensive metros.

"Anecdotal reports suggest that institutional investor interest in single-family homes for use as rentals expanded beyond expensive metros into inflationary ones, causing near ubiquitous bidding wars as a result," the Moody's report notes. "This does not bode well for the so-called American dream, a bedrock ideal that every family can afford to own a single-family home in the US."