It isn't that nobody thought of busses or trams. Its just that they are always too sparse, slow, limited in times, capacity, safety and comfort. I believe the break-even is of being able to replace cars is somewhere around a 5min schedule over the day and stations in at most 200m walking distance from everywhere.

Oh, and of course being comparable in speed to at least a bike.

That leaves only subways...

Melbourne trams are more convenient than driving and are free in the city centre. It can work just fine.