[stratelogical]

This is classic "Porter's 5 forces".

"The number and power of a company's competitive rivals, potential new market entrants, suppliers, customers, and substitute products influence a company's profitability."

There are several hundreds of thousands of restaurants (maybe millions?). There are only 2-3 aggregators. Most of the restaurants are replaceable by a similar one. So aggregators have more bargaining power.

As long as there is a profitable business model for the aggregators, the restaurants will get pushed to their lowest common profits. Without resorting to collusion with other restaurants (or asking the govt. to intervene) the only way to compete is to differentiate significantly that makes the customer desire a specific restaurant.