enacting the regulations has no direct cost to the public. Public housing is a line item on the government budget. Some towns purposely dont want to vary from the public standard b/c if something where to happen they would not have to justify them altering the standard.

Ding ding ding.

Under the modern American consensus, regulations on residential/commercial development are acceptable but public spending on housing is "socialism".

Public housing is all downsides but the costs of urban sprawl are distributed among the community and commercial development costs primarily affects developers (and it's a lot cheaper to build parking lots than subway service at a reasonable density per unit area).

How could that possibly be the case? Suppose the regulation states every new unit needs 10 parking spots--now that single unit must carry the cost of those additional parking spots.

I think sfall means "cost to the public purse". It's like any minimum requirement that the government sets - it imposes costs, but doesn't require the raising of taxes, so it's easier to do politically.