No one knows for sure -- by which I mean, a lot of really shrewd, smart, knowledgeable people disagree about the reasons. At one extreme, there are those who feel nothing is wrong, because they believe we're on the cusp of a shift to much faster economic growth, driven by new technologies like AI, quantum computing, cheap sustainable energy, and space exploration. At the other extreme, there are others who think the current arrangement is a result of regulatory capture by the wealthy, at the expense of everyone else. There is no consensus as to why.
The author posits one possible explanation: Judging by trends in corporate behavior, financial market incentives, government regulations, and federal reserve policies, the US economy has become increasingly organized around maximizing asset values and returns on capital independently of growth. Decisions everywhere are now being made, or not made, based mainly on whether they impact asset prices and returns on capital.
In my view, it's not a bad explanation.