Cuz they are? The greens is these particular setups are used to maximize performance in accordance with the stated criteria.
Let me show you something. This build is my personal masterpiece and the final result of ~70 h playing on Softcore, ~30 h on Hardcore, ~300 h of tests using 4 dummy toons, and who knows how many hours of farming with different characters during 1.9.9.6-1.2.1.5 period. Yes, the final setup uses the hard farmed double rare greens to maximize performance and to break the build’s limits. But if you can’t get the recommended greens - welcome, here is Unaffixed Ravager of Flesh, Callagadra, Crate of Entertainment and SR36 (old 90) (uncut run).
Guess what? Even if it’s a top performance build, it simply doesn’t fit the criteria of the very personal top20 topic. It’s a very expensive (in final version with max performance), very difficult to master, and the-freakin-12-bttns-flying-piano build. So, it have its own topic and I’m fine with it.