If I had to guess why there's so little money in politics I'd guess it's because there are more efficient ways to spend the money.

Political contributions right now seem to function mostly as a tax avoidance strategy. These donations are effectively free. A company or wealthy individual can either pay taxes or donate the money to a "non-political" think tank to promote policies they'd like to see.

Convincing someone to influence elections is easy if they'd pay it in taxes anyways. I'm guessing it's difficult to convince someone that their post tax money is most efficiently spent influencing the political system.

One last note, there's also many other types of interactions companies have with the government. There's state level, regulatory bodies, local and county influences. Companies interact highly with the government at the local levels because they're easier to manipulate than the federal government.