这是网上查的，在麻州为何吃饭要付小费的比较官方的回答。

because of the state's "tip credit" system, where employers can pay tipped employees a lower hourly wage ($6.75) as long as tips bring their total earnings up to at least the standard minimum wage ($15.00). Because tips are crucial for tipped workers to meet the $15.00 minimum wage, customers' gratuities act as a way to ensure these workers are paid a fair wage.