He did it to try and add a little bit of suspense to the plot, more so than anything. He wanted to give people the idea that Naruto and Sakura were a plausible romantic couple.
The problem is, however, that Naruto was always to end up with Hinata. That was evident as far back as the first concept drawings of the characters that Kishimoto submitted to the publishers.
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Of course, one didn't have to understand Taoism to understand where Kishimoto was taking the story - but the dynamics of Naruto and Hinata are directly coupled to Taoist philosophy, and it's apparent in that earliest picture, as well. Hinata is depicted in the shade of a hill while Naruto sits in the sun on the face of the hill. This is the classic explanation for Yin/Yang. Yin is the hill, Yang is what makes the hill visible.
It only made sense that the final plot would revolve around the Hyuuga - just as one of the first major conflicts revolved around the concept of destiny, the last major conflict fulfills that destiny.
Neji was not mistaken. Naruto and Hinata do share the same destiny in the end.
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"There can be no doubt."
Neji wasn't seeing his own destiny. He was seeing Naruto's - and it appeared very similar to Hinata's.
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Indeed, they share the same destiny.
This is why Hinata tripped and passed out when Naruto was on death's doorstep.
Because Kishimoto had such a predestined notion of who Naruto would end up with, it was difficult for him to write a convincing story line for him to have much in the way of a relationship with any other female. He could have made things "more complicated" between Sakura and Naruto - blurring the lines between friendship and romance a bit - but because he didn't have that as the end game, he really never paid it much more than a bit of lip-service and symbolism.
