For completely orthogonal reasons. It's not about what they sell, it's about what they do with the money. More US political candidate financing this year came from the Koch brothers than both major political parties combined. [1]

Congressional policy decisions always have to keep future fundraising prospects in mind. It is not a stretch to describe candidates who depend on Koch largesse to win as "bought and paid for." Keystone XL (a certain pipeline Koch Industries stands to benefit disproportionately from) is a controversial issue, and it ought to be considered with an eye towards policy impact rather than next year's electability.

[1] http://www.nytimes.com/2015/01/27/us/politics/kochs-plan-to-...