The real issue here is that “Android” doesn’t make phones at all. It’s an operating system written at Google and available to anyone who wants to use it. That gives manufacturers a sort-of standard they can use as a basis for their phones. They can add or subtract features, and they can use whatever hardware they can force it to run on. That means that there’s an almost limitless range of Android devices out there, many with great capabilities. However, there’s no clear standard in terms of hardware to the point where “Android” doesn’t mean much in terms of describing a device. When it comes to apps, there is a vast range of possibilities, but some of those depend on taking advantage of specific hardware or OS quirks that might disappear.
Apple sells, primarily, hardware. They provide some really nice software to run on that hardware, but they control their hardware. That means that while there are various versions of, say, iPhones out there, they have a great deal of standardization and backward compatibility. Apple also exerts lots of control over phone and tablet software - apps have to conform to a standard that minimizes the risk of incompatibilities. This irks many who want a more open system, but it does tend to ensure iPhones work the way they’re supposed to. They also sell a whole lot of copies of the same model.
That means it’s sometimes much easier and cheaper to design something for Apple products.
I’m sure Apple likes it this way, but it’s not a conspiracy. Some other company could come up with a popular device and a SDK and let people write and design stuff for their device. In fact, many companies have done so. However, developers in a free society get to choose for what platforms they develop products and my impression is that designing stuff for Apple seems to pay better.