It's not just biology, it's Sakura's pride. Her words about her >Husband< are full of love to this day, I find that so hard to believe if he really had an affair with another woman before her and dropped the baby on Sakura and left them for many years. Notice Sakura still cherishes that forehead poke, and what were Sasuke's words? "I'll see you when I am back, thank you", he promised her and now they are married.It's just ironic that her biology is all the fans really care about. kinda funny
It just doesn't add up if Sarada is not Sakura's daughter, it's too cruel on her.