If everyone needs to have a car to get around that's 3 parking spaces per person. Or 6-12 parking spaces per household.
This is nearing the square footage of an apartment to house the same number of people. So for any given unit of housing real estate we need an equivalent or greater amount of parking real estate.
When everyone wants to live close together (ie in LA near where they work, socialize, etc. not in middle of Nebraska) that puts a real pressure on space, and drives up the cost for real estate.
Even if you want to increase density by building higher buildings, the cost of those condo/apartment towers now must factor in a parking garage pedestal taking up 1/3 of its height, and so must offices, shopping centers, etc.
I don't think the ratio of parking spaces per car needs to be reduced. Rather it needs to be recognized, and thus reveal the cost of policies that lead to one car per person. If you can reduce the cars per person ratio, you reduce the number of parking spaces required at a 3x rate.