Because in Yaniv's delusional mind it wasn't supposed to turn out like this. He thought surgery would give him a real working vagina. He pictured having actual female genitalia, so close to the real thing that even doctors wouldn't be able to tell that he wasn't born a biological woman. He's so removed from reality, that right after surgery, when what was left of his penis and balls was already an infected mess, he was still convinced that he had been given that pretty little "coin slot" pussy he idealized. It's only because it's all gone so unbelievably, horribly wrong, to where the part of his penis that was supposed to be his clitoris has literally fallen off, and whatever is still attached has become a seething, reddish, greenish, blackish pile of goo, which likely causes him constant pain and nausea, that he even realizes that maybe he fucked up and that he didn't get that perfect little pussy after all.