It's not just vote-buying, it's also buying support for the project. They cite an example where some transit stations started simple and became more and more complex. I've seen this happen with local transit projects where basically some NIMBY or supposed "community group" shows up and places all kinds of demands that wildly increase the costs of the project. There is either a lack of appetite or a lack of authority to tell these groups to fuck off, which results in enormous cost overruns.