He used the toll revenue to fund his own highway building projects, independent of state/local budgets.
He fired everyone on his staff that advocated for rail network. He starved rail lines (that, at the time, were being used very heavily) in favor of road networks.
He also rather hated black people and puerto ricans.
I can only imagine you've heard things about Robert Moses written by the great fans of the man, who USUALLY were high-modernists who loved his big bridges and roads.
his biography, "The Power Broker: Robert Moses and the Fall of NYC" is the comprehensive evaluation of his life and legacy. He shaped the modern world 10x more than anyone else who has ever lived, and vastly for the worse.