Because it's economically infeasible to drive?
It's economically infeasible for a large percentage of people to drive in a dense urban area, period.
That's true even without congestion pricing. A city would go broke and bulldoze itself trying to add enough stacked lane, highways, and parking to handle everyone who would prefer to drive in or through if the capacity existed.
It would be before the congestion fee anyway - parking costs alone are absurd and cumbersome right?
Well yeah — cars are expensive.
That was the case before congestion pricing too.
Yes, but also it's just annoying to have a car in NYC. For many routes the subway is going to be faster than driving and sitting in traffic, unless you're traveling between outer borough neighborhoods that only have a connection in Manhattan. If you're making that commute often (say, Bushwick to East Flatbush, or Flushing to Canarsie), a car might make sense, but then this whole congestion pricing thing doesn't apply to you.
Transit is $3/ride (in a few weeks), 24 hours, and all over the city. It's not perfect, but for the vast majority of cases owning a car in NYC is just not really worth it. If you need one because you have a weekend home out in Long Island or up in the Hudson Valley, you can afford the $9 toll.