That's what I hint at with "basic economic theory". Evil Corp X wants maximal returns and there is a price point at which they get maximal returns. They can't just raise prices infinitely, because nobody will buy the service. If a middleman takes a cut then that optimal price point moves. Explaining it as the cut being shifted onto the consumer is too simplistic of a model. A part of the cut is shifted onto the consumer and the rest is lost by Evil Corp B, to maximise their total revenue.
although wholeheartedly I agree with your sentiment, that's where our opinions diverge... none of the parties mentioned in the original issue are 'wanting to do good' in my opinion, even thoug it _is_, as you say, understandable that they do what they do.
Yes, for the immediate issue at hand they just want to make money right, but they might be seeing their greater mission as extremely good, for example in providing the best handheld computing platform to the world or whatever it might be and that makes it all OK. To which level that is delusional thinking I'll let you decide for yourself, but I have a lot of first hand experience of how the mind operates in top level C-suits. They almost have to fool themselves to be able to operate and at their core believe without a shred of a doubt in what they do. Whether this comes from starting each morning with Tony Robbins affirmations I do not know.