And technology has little to do with this change. Plenty of places are still trying to run bus services. Because ubiquitous cars still aren't. But all the intervening challenges have made that near impossible to do (cost)effectively.
Similarly the theatre is gone because once zoning presses you into a car to get there, what's the real difference between 5 minutes to the local downtown or 15 minutes to the multiplex at the mall?
The root cause was largely a socio-political failure. Self-segregation, myopic zoning, a belief in perpetual growth all abetted by enough wealth on the part of the builders to not care about long term efficiency.