I'm wondering about the move order 2. d4 cxd4 3. Nf3 in Sicilian. If black does not try to protect the pawn and plays some normal move like 3... d6, 3... e6 or 3... Nc6, then 4. Nxd4 transposes into one of the usual lines. On the other hand, 3... e5 does not seem to be the option, as e. g. white can play 4. c3, and if black captures on c3, it's a Smith-Morra gambit which black has already messed up by playing d5 in one move.
So, are there any options for black that are better than transposing to the main lines? If not, I'm wondering why this move order is much less popular than 2. Nf3.