One interesting conclusion he draws:
I suspect the real reason is theology. Just as religion frequently involves simplistic good/evil comparisons, members of the church of free enterprise frequently hew to the first (Thou shalt not unionize) and second (Thou shalt not bow down before Democrats) commandments.
They do so, Gross adds, without regard for facts and contrary evidence (which he documents in his article). (See full article.)
I propose a theory of my own. Corporations cannot be separated from the individuals that run them and these individuals, with some notable exceptions, are mainly driven by their own greed.
While business can prosper under Democratic administrations and Congresses, the individuals that run corporations fare much better under Republican administrations (because Republicans always slash taxes for the wealthiest individuals). And since compensation for CEOs is really not tied to the performance of the companies they lead (as proven by the obscene bonuses that CEOs reap no matter what their companies' results) there is no incentive for CEOs to contribute to the party that creates the best conditions for business, instead of the party that allows them personally to make away with most of the loot.
In the end, it's all about greed.