Why is it any different from "we want an asphalt parking lot but it's not worth the asphalt cost" or "we want a giant sign but the pole to hang it on is too expensive" or "we want an asphalt parking lot but renting the machine to paint the lines is too expensive" or "we want to be open 24/7 but we can't afford to cover third shift"?

Because this is a constraint we've imposed upon ourselves to the detriment of the public. It's like how you have all sorts of workplaces with absolutely moronic rats nests of extension cords and power strips and whatnot because you don't need a permit to plug stuff in. They're following the rule and arriving at a stupider worse solution and we're all poorer for it. We could literally be richer at the stroke of a pen. Whereas to make paving cheaper we'd need to make technological progress.

Nobody's interests, except some spreadsheet pusher who's missing the big picture, and some idiot ideologues, are effectively served by putting a ton of "built to the bare minimum" green space that the users don't actually want anywhere the economic potential of the land supports more density of actual use. And if you have that density there's more than enough money kicking around to manage your stormwater more cheaply than piecemeal private solutions (basically all the same pro/con as septic vs sewer but with less digits in front of the decimal).

Yeah it's nice to have parks and recreational green space, but those are planned to be fit for that purpose. The catchment basin behind the shopping center's parking garage is only fit for making the parties that got to construct and maintain it a little richer.