There are many reasons, but the top of the list is Sarbanes Oxley. Regulation and the rise of secondary markets has made it such that retail investors no longer get access to companies during the higher risk, higher reward phases of company development. Apple (1980), Microsoft (1986), and Amazon (1997) went public with market values ranging from $440 million to $1.8 billion. Because they listed so early, public market investors were able to ride those companies up by 2,000x to 6,000x over the following decades

https://a16z.com/where-have-all-the-ipos-gone/ https://jhfinance.web.unc.edu/wp-content/uploads/sites/12369...

This is why I am very skeptical of complex regulation, because even if it is well intentioned, more complex regulation usually favors the rich and powerful. SOX was sold to the voting public as protecting them, which it did but at a very real cost. I became an accredited investor to get access to higher return, higher risk opportunities. It's a shame your typical 401k investor can't have 10% of their portfolio in higher risk assets like me.