Developers won't cut their own throats by providing too few spaces. There is a lot of resistance to parking reforms. Makes projects more marketable. No administrative apparatus. Carpools require on-going support.
Parking is perceived to increase the marketability of projects and is risk-free.
Bankers are also reticent to go below code standards for parking. Transportation planners often call restrictive parking policies, higher fuel prices, etc. This is actually a misnomer. Place solo-commuting and vanpools on equal footing. One of the saving graces of traffic congestion is that it is self-regulating.