Because Black usually has no trouble in the ensuing endgame after the queen swap.
BTW the position you posted in the diagram is extremely uncomfortable for Black after 14.h5 Nxh5 15.g4 Nf6 16.Kb1 (Karpov's 16.Nde2 is also very awkward to meet). You'd better look for something else instead of suffering in this position.
I play Sicilian as Black.
I know that there is a Rxc3 in this variation of Sicilian Dragon and there is also Bxg4 when white plays g4 and then black plays Nxe4, opening the diagonal of the g7 bishop. I don't know when to play it.
I tried it while playing blitz but didn't get mating attacks.
What are the conditions i must keep in mind while doing these sacs? (Sicilian Experts, please help)
When Black plays Rxc3, why don't white play Qxc3? In all the games I played, they play bxc3.