Rich people are more likely to pay accountants to come up with complicated ways to exploit the tax system. If the top 5% had access to this loophole, you’d probably end up with some crazy outcome like 80% of money saved from this deduction goes to the top 5% of earners. And that would make the provision more expensive to include in tax legislation (trading off against other things like the headline tax rate). Since “no tax on tips” was a campaign promise, they probably wanted to keep the promise while setting limits to make it easier to fit into the rest of the bill.