First off, not "everyone" was on MySpace. At its peak, MySpace boasted 100 million accounts (not active accounts, just accounts created). When G+ launched, Facebook claimed some 600+ million accounts. This is important, since it meant the market was mostly saturated. Facebook picked up many social network newbies, while G+ came into a market where most people who wanted to be connected, already were.
Secondly, MySpace was a lot more customizable than Facebook, visually. Facebook's apps weren't really "customizations", as much as more features the platform offers. I agree with you that apps were an important feature for new users for quite a while, but at least from what I can see, they're a relatively minor part of Facebook feeds these days (at least in my vicinity), with the status updates, pictures and Pages taking the lead.