It’s free money. You spend 3billion and have more billions drop in from investors. You get to create great tech and then make 100s more billions drop from IPO. When the initial investment is a rounding error in your portfolio, it’s a crime to not do this
Realistically if they were capable of being happy doing something other than acquiring more currency they would never become billionaires. Any reasonable person would simply live life enjoying their 10s or 100s of millions.