It is probably not always as simple, or even as logical, as that. For one anecdote, Planet Money did an interesting piece following the motivations of an inside trader: 671 - An Insider Trader Tells All (https://www.npr.org/sections/money/2018/03/23/596533461/epis...). As mieseratte says in another comment thread here, "it's not black and white as you paint it." What I'm saying is, that one of the (perhaps uncountably many) driving forces of corruption might be misplaced altruism – a few skilled con men who know how to present the right argument to persuade others. To hack their neural network, if you will. Or another answer might be: "why not? it was possible to do". Another recent episode to follow a similar line of investigation would be "Episode 685: Larry vs. The IRS".
It seems like US politicians are plagued with it. I consider constant giveaways to the wealthy while mostly ignoring the majority of the population to be corruption, like this recent tax bill.