My mom (who is 97) has a vivid memory of seeing FDR in 1935 -- the whole extended family took the the Red Car from Compton to downtown to see his motorcade. She remembered the electric trams worked really well, especially for folks without much money.
The main reason as far as I'm aware was due to intense lobbying from car companies. It makes absolute sense from the perspective of Ford, etc. to have alternative modes of transport be removed from the streets