I was researching the Sicilian opening and something interesting stuck me.

1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6, why is this step not followed by Nxc6, which would leave the opponet with two choices, takin with the 'd' pawn might endanger black's ability to castle and taking with the 'b' pawn will isolate the 'a' pawn. This move might also apply pressure on the knight on f6 going forward.

Far from being a master, I am not even a registered player so my analysis might be way off...

But, taking my analysis to be true, I have a question for you...

My friends, the question is, is this move a popular option, if not, why so?

It is not popular, and for good reason. First of all, taking with the d-pawn is totally fine. After white trades queens black can put his king on c7 where it is safe and also conveniently close to the centre, incase further simplification occurs. Taking with the b-pawn is what I have done as black in this position, and it may be even better. Black gets a large mass of pawns in the centre of the board, which may not seem significant right away, but eventually will pay dividends. Also, white has already moved that d4 knight twice, so trading it for a piece that has moved once is bad in principle.

i think white does not want to take because black can take bc and black will have more pawns in the center and be able to equalize with d5 easier