Look man, now you're just being obtuse. Are you seriously suggesting that major corporations and those who own them are collectively pouring billions of dollars into political campaigns out of simple altruism? Please tell me you're not this naive.
No, the officers of many of these corporations actually say they're investments- at least in private settings and unguarded moments.
They feel like they get their money back tenfold in terms of access and influence in legislation ranging from tax breaks and subsidies to preferential treatment.
Agricultural subsidies are an excellent example; the vast majority of Ag subsidy money goes to major corporations instead of individual farmers. How do you think that happened? By accident?! No! Cargill, ADM and many others got deeply involved, and one of the ways they gain inside access is by funding candidates who were most likely to be open to their point of view. After the election, those same politicians found themselves bound to listen to and support the agenda of their major contributors- or risk losing that funding to opposition candidates in the next election. Big Ag is anything but alone in pursuing these practices.
Finally, if they do well for their corporate masters, they get rewarded with fat 'consulting' contacts, often worth millions, when they retire from public life.
Every major industry plays the same game, to the point where it's considered a standard path to wealth by current and former politicians.
It works in reverse when it comes to regulatory agencies; the practice of hiring leaders from within the regulated industry has led to regulatory capture on a vast scale. Goldman Sachs CEO Hank Paulson, Timothy Geitner among others have been Treasury Secretary, and for some strange reason under their tenures Wall Street has benefited while middle America suffered.
The notion that all that money is somehow given without an expectation of return is laughably backwards.