Both. I don't think Microsoft's developers are anywhere near as talented as the ones Sony's got locked into developing for their platform.
There is nothing on Xbox that even comes close to the likes of Bloodborne or Shadow of the Colossus. I don't really know to how to describe it, but Microsoft's games lack that.. something that elevates many of Sony's exclusives to such incredible heights.
Having the best Japanese developers on their side probably has something to do with it.