As an example, suppose ACME, Inc has $1 million to invest. What should it do?
It can invest $1 million in the free market and its management believes that will yield a 20% return on investment, i.e., it will end up with $1.2 million.
As an alternative, management perceives that it can invest $1 million in the government which will then pass tariffs against foreign competition. For the average american buyer of the ACME's widgets, this will mean $1 in higher prices in widgets. If there are 2 million buyers, this means $2 million in revenues for the corporation. Its return on investment in the government will be 100%.
Note the difference between the amount of cost to each consumer vs the profit for the corporation.
Whether the ACME invests in the free market or in the government will usually depend on where management believes the return on investment is higher.
It is in a politician's interests to cater to corporations because the money invested by corporations in government is needed to run campaigns, advertise, and win elections. Politicians can afford to do this because voters won't get angry at such a small rise in prices. They'll barely notice it. But the corporation will notice the benefit of the large return. Why play fair in the free market when it can bend the rules via the government and achieve a higher return?
This strategy is not just open to corporations, but also to any group. A union can bribe politicians to pass laws that ward off competition from other workers. The costs that the average American incurs are very small individually, but the unions benefit greatly through increased job security from the captured monopoly on labor. The same tactic can be used by any special interests group - trade organizations, environmentalists, moral authoritarians, etc. It is often in these groups' interests to invest in government for a focal benefit whose costs are dispersed enough that it doesn't hurt the popularity of the government in power.