For example, if Archer Daniels Midland's CEO Dwayne Andreas used goons and violence to stop people from buying sugar from Caribbean producers so he could sell more corn syrup, he'd wind up in jail. If he makes big campaign contributions, he gets the same result, without risking imprisonment. Congress just enacts quotas and tariffs. Rent-seeking is inefficient. But to have such an open and above-board wealth transfer would have been politically impossible.
Some campaign contributions represent extortion.
It's the bad cop-good cop sham. One congressman tells a CEO that another congressman has a bill pending that's going to be very costly to his company. It might be environmental or worker-safety regulations, import restrictions, etc. The congressman tells the CEO that a fat campaign contribution will help defeat the bill. Forget about campaign finance reform.