Why isn't 6. Be3 popular in this Sicilian Defense line? Why isn't 6.Be3, with the "English Attack" idea, really popular against 1. e4, c5 2. Nf3, Nc6 3. d4 cxd4 4. Nxd4, Nf6 5. Nc3, d6?

[FEN ""]
[StartPly "10"]

1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 d6 6. Be3


Although it's very popular against the Najdorf and Scheveningen variations? Is ...Nc6 that strong, compared to ...e6 or ...a6?
There is the following line, similar to what happens if black reacts the same way in the Najdorf:

[FEN ""]

1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 d6 6.Be3 Ng4 7.Bg5 h6 8.Bh4 g5
9.Bg3 Bg7


This is a mess, but Yermolinsky argues that the extra developing move (...Nc6 instead of ...a6) black has compared to the Najdorf version should make this relatively better.

So if white wants to play the English Attack here, it is more usual to play 6.f3 first and only then Be3.

But there is another reason that is at least as important: 6.Bg5 (the Richter-Rauzer attack) is really good, and there is no good road to equality known for black, as far as I know.