Founders often run their companies better
https://hbr.org/2016/03/founder-led-companies-outperform-the-rest-heres-why
Specifically, the study found that S&P 500 companies where the founder is still CEO are more innovative, generate 31% more patents, create patents that are more valuable, and are more likely to make bold investments to renew and adapt the business model — demonstrating a willingness to take risk to invent the future.
The "spread it out" doesn't get spread out to society, it will get spread out to other venture capitalists and hedge funds, and they are never as interested in the long term vision and plans for the company as its founders are.
Saying, sorry, you can't run the company the way you want after a certain size (edit: within the law obviously), is just plain shortsighted.
I'm not saying don't tax them when they try to realize those gains via selling or borrowing, and it can even be at incredibly high rates, but stealing the company from them is not the right decision. Make them choose, their company or the wealth it generated.
Edit: And just to be clear - yes you can be a CEO without any shares, but without your founding shares giving you influence, you won't have the same kind of influence within the company, ultimately neutering your ability to function the way you'd like and stiffling whatever vision / passion you might have.