See, you can be a good songwriter, but you still have to sing it. And his singing distracts me from everything else. For something to be a masterpiece, all parts have to work together, so what's so great about Bowie?
It's the same reason why I'm Beatles over Rolling Stones. The Rolling Stones are classics, sure, but they're raw and rough around the edges. Fine for representing rock and roll, but the Beatles are just more pleasant to listen to. Music should be pleasant to listen to (or at least not be irritating), and I don't find David Bowie pleasant.
Personally, I'm not very into modern music as much (pop-wise). I do agree that Beatles are much easier to listen to that some other bands. But everyone has different tastes. For example, I'd rather listen to a Hans Zimmer soundtrack over any "popular" music made this decade any day.
Spoiler
Heck, it doesn't even have to be Hans Zimmer! I'm also fine with John Williams, Martin O'Donnell, Two Steps From Hell, and even Arata Iiyoshi.
Like I said, everyone has different tastes in music.