I don't fully understand it myself, but option B isn't even an option because hiring an internal team means operational expenditure to pay for it, while contracting an outside agency means capital expenditure is used to pay for it. No government or large corporate will do what you're suggesting due to this, even though to those who aren't accountants it makes absolutely no sense.
I'm not sure how much easier the RFP process could be as well, either. At least here, it's just a matter of looking at the detailed RFP, and submitting a tender into the box with your estimates of cost/timelines/product options, and just make sure to check everything off on the checklist. Now, I have heard of instances where the checklist is written in such a way that they may as well have an unspoken checkbox that says "be Microsoft" or "be IBM", but those are fringe cases.