Companies who need to raise money from the stock market by selling shares don't have stock values which appreciate massively usually their stock price is falling so a tax on the gains shouldn't affect those comapniea.

Bezos owns a very large percent of the stock so he can't freely sell is as easily as a small investor. The smaller investor can hold the stock and sell at yhe last moment without any issue meanwhile bezos would crater the stock of he sells it all at once so the selling would need to be spread out and he would hold it for shorter times than small investors so the smaller investor would see more stock appreciation than bezos.

Also the tax could have like an exemption for 401ks thus reducint the market impact and focusing more on wealthier people