"Jasper can try to convince property owners that parks will increase the value of their property, so they should just build them for free," writes Lydia DePillis, "It's a pretty tough sell, though."
She then goes through other possible ways to encourage park-building in an urban infill neighborhood where development is springing up. But the difficulty of persuading nearby landowners to foot the bill should be a sign here. People like living near parks and people also like having more money. If it's not possible to persuade landowners that the extra value of a park will exceed the extra cost of the park, then probably the park shouldn't be built. To be sure, one can argue that some parks are important citywide amenities with large nonlocal externalities. Those are the kind of parks someone might deliberately travel to from another neighborhood in order to hike or play sports or whatever. But a small park in a newly-built neighborhood is basically a private benefit for the developers of the surrounding properties. If they want to pay for it, that's great. But if they don't want to, I'm not sure why finding a way to get one built should be an urgent policy priority. What touched this off was a change to the D.C. budget that took money away from park-building and gave it to low-income housing construction instead, and that seems like a very sensible tradeoff to me.