They did it for those people who are more into traditional video games. My little brother wouldn't know how to play a game like this but give him a challenge like having to unlock object and he'd play until he'd done them all.
~dizi
I can appreciate that different people have different playing styles. I just wish they would have provided a cheat code so that those of us that don't want to bother with the "challenge" could just mass unlock all the goodies.