The reason is marketing. If your website sells you as the perfect fit for everything from embedded systems to web apps to iOS to Android, you are going to have

The reason is marketing. If your website sells you as the perfect fit for everything from embedded systems to web apps to iOS to Android, you are going to have a hard time to stick out in any pile of candidates-for-our-next-project. If however you wrote a book on iOS development, have a few dozen in-depth articles on Objective-C and Swift on your blog and can refer to a handful of your apps in the app store, you will at least be on top of the (lucrative) pile of candidates-for-someones-next-iOS-project.