Billionaires do not get a tax exemption
Once the money is in stocks, it doesn't get taxed unless you draw on it, but the billionaires can use strategies like buy, borrow, die (which last I checked only really works if you're north of ~ $300M) to avoid personal taxes.
They also operate at a scale where many tax breaks become viable. CEO owners aren’t paying themselves nominal salaries because they are actually working for free. Creating a shell company to own your 50k car isn’t useful but it’s damn well worth it if you’re buying a 50+m dollar yacht for personal use. Turning depreciation into a nominal loss offsetting capital gains etc.
Meanwhile people of lesser means get stuck with all kinds of crap like a 10% early withdrawal penalty on 401k plans.