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.

They won't pay accountants, they'll tip them!