Beats me why.
Sandler was cute, some 15 years ago, when he was new to the movie-making business. Much like Jim Carrey, his facial expressions and moronic voice became his trademark but, in contrast to Carrey (who still finds it in himself to change his brand from time to time and remain relevant and funny), Adam became deja vu.
So, nothing new here. Same old. Even the plot - use a female friend to get the girl but decide that the friend is the one you want. Aniston/Sandler combination is not the worst, but it's not the best either. And as much as I appreciate her post-Brad Pitt survival tacticts, she's too stiff to pull it off. Sandler's too lame to turn the movie into an enjoyable one and Brooklyn Decker (who we all know as a swimsuit model and Andy Roddick's wife) is exactly what you might think: blonde, untalented, intellectually limited but with the boobs you can use as weapons and absolutely no waistline. Oh, and Nicole Kidman makes an appearance, a pale one at that (both physically and metaphorically).
5 out of 10 (at least there's no Rob Schneider here).