Why does everyone play this move?


You study the open sicilian. That is the closed sicilian. In the closed sicilian, niether side wants to develop their knight in front of the f-pawn.
Don't ask anymore, I got it from a book. I'm a 2N expert, not a sicilian expert

Yes it's closed sicilian. Here's one of the line I know;
Notice how niether sides developed their KN in front of the f-pawn.

They say 2 Nc3 fits better with low rated players, because the ideas of the close sicilian are rather easy to understand, maybe that is the answer to your question.

as a sicilian fan you will over time have a wide range of moves in your knowledge regardless whether white goes knight c3 , or even c2 c3 ,
the sicilian is a potent weapon for black and has stood the test of time and whites attempts to refute it ,
dont worry just keep studying the sicilian it will give you a lifetime of good chess

yes Huey i agree i look at the sicilian as a mistress
look after mistress siclian and she will look after you ,
but wrong her and pay the price
its taken many mistakes to get to the point where i can represent her fairly well
she is happy for now

The original question is why do they play Nc3 instead of Nf3. Having taught kids at this level, I can tell you the reason has nothing to do with open versus closed Sicilian. It is simply that the knight on f3 attacks nothing and defends nothing. They know at this point 'knight before bishops,' and they choose the knight that does something, in this case it defends their e pawn.