Or they appeal to even more console gamers and get even more money. They're also making the console versions similar, meaning they aren't taking advantage of the advantages both the PS3 and 360 offer over each other.. so why should they make an exception for PCs?
Why would not releasing content on PC make something appeal to console gamers more? Do you really think there are more console gamers who are willing to buy something out of some misplaced hatred of a platform than there are PC gamers?
As for the second question, because the difference between the two consoles, and the difference between the consoles and PCs, are in different orders of magnitude. The consoles are effectively as powerful as each other, a half decent gaming PC is a dozen or more times as powerful. The two situations are not comparable.