Rosa Parks was a militant activist and part of a large activist network that was consistently staging public acts in defiance of Jim Crow segregation. This is misleadingly left out of most folks’ intro to her most successful action.
My school system was always big on emphasizing that there were pre-cursors to Rosa Parks (like Claudette Colvin), but they didn't have the connections that she did to make it happen.
Another factor is that the black people that were mainly affected by the segregation were the primary funders of the bus system. Their boycott was incredibly significant to the bottom line.
