Physically making progress on a project makes it much harder to undo due to loss aversion and the sunk cost fallacy.
In The Power Broker, we see an example where Robert Moses learns that by intentionally underfunding a large scale project to make it easy to pass but taking the first steps to physically build it, officials had no choice but to continue to support it financially. Officials facing elections would need to stand before the electorate and undo what was already done (not just on paper) and therefore take an unfavorable position that could cause them to lose their place. Essentially this would force officials to go against building parks which would be hugely unpopular.
Once you sink that first stake they’ll never make you pull it back up.