Accelerated Dragon Maroczy Bind 10. Nc2

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Zraxlu
In this position, why does theory say to play Bd7 before Nxd4? Doesn't this allow white to play Nc2? Normally against Nc2 instead of Bd7 I play Nd7, Nc5, and f5 and get comfortable positions, and this move order would interfere with this plan. I used opening databases and can't understand how black plays after 9...Bd7 10. Nc2, can someone help? The 9...Bd7 move order stops white from playing a quick b4 and it would be nice if I could play it.
chessterd5

10..., a5 looks interesting