Yeah well, pop was jazz in the 40'ies, rock'n roll in the 50ies, Beatles in the 60ies, Zep ect. in the 70ies, Van Halen in the 80ies, Grunge in the 90ies, electronic music since the 2000s, maybe now it's the DJ wave..

I think what sells depends on what's coming out fresh in a particular decade. It has to do with culture, technology, fashion, discourses ect. Pop is simply just in tune with the times, in sync, in harmony ect. If you get the vibe, you get to jive :-)

Stay tuned to whats happening in the world, pick up the young generations attitudes towards it, and emotional reactions to change.. and write, for it, against it, along with it, anyway you feel should turn out great music..