Because we - the plebs - are here to provide liquidity for the risk-takers. Hence whey they have to IPO.
But for what it is worth, for every successful AI company like Anthropic, OpenAI, etc. - there are probably tenfold more that are valued in the low billions, and will be the first ones to wash away / become worthless if/when the bubble pops.
And lastly, private sales do exist.
Increasingly these days, it seems if a VC backed company was profitable it would never IPO.
Why would they want to share profits?
In these companies, the shares *are* the product. Just like on social media *you* are the product, not the content.