I think because Loki is curious and never fit into Asgardian society it kept his mind open to new cultures and understanding. Where Thor is an Asgardian hero and fits in his home world. Also Loki is like 10 times more intelligent than Thor.
I think the movie would have ended differently if Loki said yes to that drink. XD <~ actually, in the original script he did take the drink. He said "another," screamed "come at me bro" and Tony drunkenly stumbled out the window.