Probably nothing.

It seems quite reasonable that unrealized capital gains would be treated differently for "a primary residence" vs "a multi-billion-dollar stake in a company controlled by the owner."

A far better question is: Why does my company pay me in cash (40% marginal tax rate) instead of "equity shares of 'special partnership units' representing the value added by verteu's labor" (20% capital gains tax)?

Or: "How did Mitt Romney's Roth IRA grow to $100,000,000 with a $7,000 annual contribution limit?"