It's not that they literally own a stake. It's that the people in their social circles have a monetary interest so perpetuating boondoggle pork projects result

It's not that they literally own a stake. It's that the people in their social circles have a monetary interest so perpetuating boondoggle pork projects results in people around them appreciating them more which results in campaign donations and all sorts of other perks. It's not quite quid-pro-quo, it's just far enough away to maintain plausible deniability. And of course there's all the people who aren't indirectly connected to politicians but who stand to benefit and the politicians will see that they benefit because votes. Look into the rules for billing hours for state police traffic details during the big dig if you want to see a good example with this. Now imagine that kind of fat in every industry that is related to a project and it's easy to see how costs go crazy.