Not surprising at all, and this was pretty much the expected reason. MGS games have a level of detail that most games can't hope to match, and when we're talking about the HD era + an open world, that level of detail gets very expensive, very fast.
It sounds like it was Kojima's sheer inflexibility on some of these things that is what really did him in. Does foliage resolution really matter that much in the grand scheme of things? Probably not. As gamers, it's great to see that he's willing to push for even the smallest details. As a business though, it's understandable how that would cause problems.