The building with which I was associated had far more than minimum required by city code, and the "excess" parking served us well as a "loss leader"; the building remained fully leased, or nearly so.
Now, if Austin were to institute a maximum parking space limit for every private office or residential building, then you'd have a major problem, especially in that the city is already competing with private parking providers in the form of metered on-street parking, municipal (taxpayer-funded, in other words) parking decks and lots, and mass transit.
One more problem for owners/operators of private real estate: hefty taxes, over and above property taxes, imposed on parking. Make parking expensive by creating artificial shortages and high taxes, and that spiffy new light rail or streetcar line starts to look more attractive.