Speech (advertising) can be bought with money. Enough advertising (money) can often buy an election.
Corporations hold a huge amount of money (= political advertising). Thanks to the conservative majority of the Supreme Court, they now hold a huge amount of electoral power, which one can expect to be used mostly to put and keep conservatives in office (who are anti-worker, anti-social, and pro-deregulation).
In summary, the logic is simple -- follow the money.