Ask HN: Why can't I make as much as I make?

In "How to Make Wealth" PG puts forward the following argument:

1. Assume a hacker can make a good wage working for someone else.

2. Assume a hacker can in turn be significantly more productive working for themselves.

3. All things being equal, a hacker should be able to make significantly more money by working for themselves (albeit at the cost of increased risk and stress).

The relevant quote: "If a fairly good hacker is worth $80,000 a year at a big company, then a smart hacker working very hard ... should be able to do work worth about $3 million a year."

My question to HN is as follows:

Excluding outliers such as Gates/Zuckerberg, is the inference that a good hacker can make more from the market directly actually valid?

If so, why does it seem most hackers struggle to capture even half their regular wage from the market directly?

All advice/experiences appreciated.