Parkland accomodates more recreators. Decision-makers and funders have many interests competing for their attention. They will most often make decisions to fund or support based on greatest good to the most people logic. Recreation, getting close to nature, getting your hands dirty, may be the best reasons to garden. They are not the best ways promote community gardening.
Parks do all of that for more people.
They're helping kids to be better kids. These are fantastic benefits. They should be celebrated. They happen because people garden together. Focusing only on the reasons why individuals want to garden as the benefits of community gardening is narrow.