>I would wager that this is a proxy for the housing market. It's correlated with renting (majority) v/s buying (minority). And renters don't want the middle. That's pretty much how I view everything I buy. It's ephemeral.

Interesting I've never thought of it that way, anyways here's a great podcast episode from 99 Percent Invisible on the "missing middle" in terms of housing.

https://99percentinvisible.org/episode/the-missing-middle/