Ok, so one company is currently making boatloads of cash(Nintendo), and the other has more money than it knows what to do with(Microsoft), and it came down to money... ugh... little babies bickering over shit they have more than enough of.
From what I've read on Kotaku and such, Microsoft offered to allow Goldeneye to be ported to both XBLA and the VC. Nintendo still refused tho. I would imagine they are not willing to allow a game from one of their systems to be ported to a competing console.