I was just reading an FT article mentioning the "inelastic markets hypothesis" that markets are predominantly driven by cash flows rather than rational analysis of value. People invest in index funds etc because the market goes up, the market goes up because people are buying. It's a bit of a bubble.

(article https://www.ft.com/content/6f549890-c2a6-4823-a095-c8ea73f7e...)