Why do we need a law telling private holders of equity how they can or can't distribute that equity as incentives?

If shareholders think the C-suite and/or board are overcompensated, they can vote for a different decision. And if they don't have the majority to get their way they can sell, buying into a company that better reflects their priorities.

I'm not sure I see the case for further regulation of what are, essentially, private decisions and transactions.