Citizens United. Nothing else to say. https://en.wikipedia.org/wiki/Citizens_United_v._FEC
Some local governments are fully designed to be perfect vehicles for corruption by this point. The incentives just lead to it over time as one corrupt prick makes things a little easier for themselves and their ilk to operate without oversight. Things compound over the decades of people drawn to the graft opportunities in local government with their campaigns funded by the beneficiaries of the graft, against little t…
... and then wonder why the public gets mad when the environmental impact study says "not good", public works says "area roads can't support the traffic influx and can't support increasing capacity due to geography and existing homes" and still approve the developer's new project anyway.