Because the only reason Kishi paired SS and NH was to cater to the manga's fanbase. I'm not gonna go into the ending, which was complete bs, but Kishi in the end was screwed either way.
I'm pretty sure NS is more popular in Japan, so that wouldn't make sense. Anyway, he said himself that he had been planning Naruhina fo a while
With Sasuke no longer burdened by his darkness, he probably grew to love Sakura; maybe he cared about her already but he suppressed it like his affection for Naruto. Also, this manga is about redemption, so it was obvious to me, long before the ending came out, that he'd be forgiven of everything
For me there was always more logic in SS than it ever was in NS. I didn't even knew NS was a thing until I came at the internet.
Sakura loved Sasuke for almost her whole life, her feelings got through the test of time and Sasuke's bad behavior. But she understood why Sasuke is acting like that. She knew it wasn't really him, that his true self was blinded by hatred and revenge.
Sasuke pushed away his feelings for everyone in order to get his revenge. He needed to act this way to put the tension in the whole story. This manga is about forgiveness and bonds. It was obvious that Sasuke will get redeemed and find feelings for Sakura again. She was the only girl he cared about since his mother had died. He admitted that in part 1.
That OVA was a filler, made by anime team, means it's not canon. Why you even consider it that? Besides the scene could be viewed as non romantic, just Sakura being sad cause she thought her best friend died. Wouldn't You react the same way?