The App Store has always had far less of a malware problem than Google Play. Apple actually has skin in the game. They stake money and their reputation as a brand on making their platform a joy to use and as free of malware and spyware as possible.

Android is sort of the default choice to enable carriers and handset vendors to roll their own smartphone platform. It's a hedge, it exists because without it, Apple coukd take Google's search monopoly clean away. Neither Google nor the handset vendors nor the carriers give a shit about UX, they've structured things so that you're kind of forced to go with them anyway.