Because they’re often paid less than minimum wage because their tips cover the shortfall. Except they lose money when they take vacation days or call out sick. Why should they be treated less than other workers who have paid vacations and sick days they can actually afford to take?
They get paid sick days, at least in ca. its law.
Paid vacation is up to the owner of the business. Waitressing is a low skill job, with low end benefits. Want paid vacation, find a job that has it.