Why 6.Nc3 in the following position in Grob opening? [StartPly "10"]

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1.g4 e5 2.Bg2 Bc5 3.e3 d6 4.d4 exd4 5.exd4 Bb6 *


In the Grob attack opening database posted in this answer the suggested next move is 6.Nc3. However, in most variations of Grob opening I looked at so far, c4 is played by White very early in the opening phase. In the above position I would pick it as the next move also.

Why is 6.Nc3 better for White here than 6.c4?
I don't think there is a drastic difference between playing 6.c4 than 6.Nc3, but from my perspective, I don't see much utility in the move 6.c4. What are you trying to achieve with 6.c4? It may seem as though you are expanding and gaining space and challenging Black's center, but Black can immediately put pressure on the d4 square with 6...Nc6 and you must defend with 7.Be3. Now, if you had played 6.Nc3, and after your opponent plays 6...Nc6, you still need to defend with Be3, but you have an extra developed piece. Note, you obviously don't want to play d5 (if you've already played c4) after 6...Nc6 since Black can play Ne5 or Qh4 and will have a better position than White. I'm no chess expert, but those are the very small differences I see.