There is only so much physical space for transit infrastructure. In many cases, unless you're going to cut down people's homes or businesses, you will be trading off from one mode to another. Exceptions are things like unused green spaces under subway tracks (looking at you, Caltrans) and things like that.
There's also the social design component: making driving uncomfortable increases the relative comfort of public transit, meaning people would be more likely to choose the latter over the former, improving the chances of a critical mass of public transit utilization.