1. Apple doesn't make money off of apps, they make money by selling hardware. Their only interest in having a locked down app-store is so that iOS will be perceived as the "safe, virus & malware-free approach". I know it's really hard to understand how a company can make money by selling real physical objects because we've all been so conditioned into thinking that you can only make money off of software and ads.
2. iOS is a gigantic market. Android has more users but those users don't have any money. Dramatically more money is spent by iOS users (on apps and everything else) than by Android users. You are incredibly naive to think that iOS is not a big enough target for virus/malware authors.
3. This is how I know you're a child, because you think that if there's a tiniest chink in the armor then the armor is useless. It's really common for kids to have this perception because their brains are under-developed, can't see shades of gray, and thus can't comprehend that there can be a lot of value to imperfect security. Hopefully at some point in your intellectual development you'll understand that ALL SECURITY IS IMPERFECT. As of right now your brain is just not capable of processing that.