Idk why this is such a mysterious or unexpected thing. Housing construction crashed through the earth following the subprime crisis and the deficit in available housing has not yet recovered. Prices are up due almost entirely to supply and demand. Current pace indicates the problem will probably sort itself out in a few years barring any further disaster. Some YIMBYism could speed it up.
I assume you're referring to the graph on the page you linked. Is there an explanation somewhere of exactly how it is calculated?
I tried to read the "article" underneath the graph but it just seems to be a disjointed collection of assertions strung together with inappropriate connectives and insane formatting.
The caption is a little vague, but it says the source is census data by which they mean the US Census Bureau which does an estimate of housing every year.
Moodys has a more technical analysis if you have patience to read it all using both census and realtor data:
https://www.axios.com/2023/12/16/housing-market-why-homes-ex...