I don't view the lake promenade a main street. I see it as, Frontlot: Town square, Studio one : Main Street, Hollywood boulevard: Main Street continued. With the tower of terror and Floor rosette being the parks hub. I see the promenade as an additional area, sort of like the street after carthay circle in DCA that's between cars land and avengers campus leading up to Pixar Pier.
The problem is dat Studios lacked green, trying to increase that percentage by throwing everything into one single lane is a choice. But it is probably the main reason for not building a Hollywood version of main street. I think a more quite green space instead of another busy area is a welcome addition for Studios.