There's a lot to be puzzled about on that list.
Two Miles Davis albums are the only jazz entries. The totality of country music is represented by Johnny Cash at Fulsom and Loretta Lynn (and the Burritos if you count them as country). No folk music or even folk-rock at all. A single Fela Kuti entry represents the whole African continent. A single Kraftwerk and Can album each (neither of them their best) represent the whole of Europe. Nothing at all from Asia ... And yet Big Star has three entries! Had anyone really heard of them before they started getting name dropped by everyone a decade or so ago? Then there are swathes of distinctly mediocre R&B/rap from the last few years that, while undoubtedly popular surely can't be considered top 500 (or even top 5000 material).
And why oh why do
Pet Sounds and
What's going On always top these sort of charts? Really? The best albums ever?