Suster points out that the longer the company stays private, the more valuable it becomes. And if during this time VC’s can hold onto their pro-rata (fancy word for what percentage of the startup they own), they can make a ton more money.
The premise of Growth capital is that if that by staying private longer, all the growth upside that went to the public markets (Wall Street) could instead be made by the private investors (the VC’s and Growth Investors.)
I think the implication of the question may have been "why not just hold the stock after the IPO if you expect.
Further down, continuing the Sister quote:
three examples Suster uses – Salesforce, Google and Amazon – show how much more valuable the companies were after their IPOs. Before these three went public, they weren’t unicorns – that is their market cap was less than a billion dollars. Twelve years later, Salesforce’s market cap was $18 billion, Google’s was $162 billion, and Amazon’s was $17 billion.
If it stays private, not only do your existing shares appreciate (which would also happen if it was public), but as an existing investor if you have pro rata rights, you can buy more shares (vs them being sold in a public offering) increasing the number of shares you have that will appreciate.
