The Montgomery Bus Boycott was like a giant "off switch" for the city's money. Since most of the people who rode the buses were Black, the bus company started losing massive amounts of money every single day as the seats were empty. Because the company wasn't making enough money to pay for gas, drivers, and repairs, the city government started to panic about the whole transit system collapsing.
It wasn't just the buses, though—it hit the local stores, too. Since Black citizens were walking or carpooling instead of taking the bus to downtown shops, white business owners saw their sales tank. These shop owners started putting pressure on the city leaders to just end segregation already, because losing money was becoming a much bigger problem for them than keeping the racist bus laws.