Because it takes hardly any of the real world constraints into consideration. If you're designing for the 15 artists / albums in his mockup, then yeah , this is fine. But that's not the real world case.
Also things like qualitative user testing, a/b testing would go into every single pixel of his design. I am not particularly sure if the most important separation of the music listening population is into hoarders vs nomads. You'd evaluate that, make a decision. Things might get muddled there.