because Shang was too scared to make a move, remember? Mulan had to invite him to dinner!

hintedy hint hint, SHANG!!

How come Shang and Mulan?

^ Because there's little romance in their movie (which is okay) so we want him to kiss her..

or tiana and naveen

I think this is what the carpet was thinking to himself when Aladdin was dropping Jasmine off at the balcony.

Aurora/Philip because we want him to save Aurora from Malificent's spell by kissing her. Also, it was because he wasn't sure how he truly feels about Aurora.
Mulan/Shang and Belle/Beast-both Shang and Beast were shy toward thier women. We want Beast to love Belle b/c part of that will decrease his spell. (Belle's love for him will add in to break it).
Like someone else said, Shang was shy-he wanted to say something more to Mulan after she saved China, but he stuttered. Mulan had to make a move by inviting him for dinner, we hope that Shang will kiss Mulan.