It's called the political economy: Politicians use the taxpayer to subsidize businesses, and then they demand money from those businesses. Retired congressman Barney Frank, the Massachusetts Democrat who used to chair the House Financial Services Committee, was fairly explicit about that connection, regarding the Export-Import Bank.
Congressional battles over the Export-Import Bank and terrorism insurance are an opportunity for Democrats to win back corporate elites who abandoned the party after the passage of the 2010 Dodd-Frank financial reforms, according to one of that law's primary architects, former Rep. Barney Frank (D-Mass.).
"I think this is finally starting to get to the business community now," he told HuffPost during a July interview. "Part of this was the real significance of the defeat of [then-House Majority Leader] Eric Cantor. Eric Cantor was one of [Goldman Sachs CEO Lloyd] Blankfein's best friends in government. His wife used to work [at Goldman] and they were personally friendly -- of course, a great recipient of money. And then Cantor loses and now Kevin McCarthy shifts his position on the Export-Import Bank."
Read the whole article. I think Frank's description of the relationship between Wall Street and the Democrats is very accurate. In short: Big Business supported Obama, but then even though Obama didn't really hurt Big Business, he hurt their feelings by talking about Fat Cats, and this (and Romney's candidacy) swung Big Business back to the GOP. Now that parts of the GOP are being all free-enterprisey, they're driving business back to the Dems.