But people do develop for iOS. It must be worth it on some level. When it's not worth it, people don't develop apps. Look at Blackberry and that other failed one, can't remember the name, bing phone or something.
Seriously though, I almost felt sorry for Microsoft this weekend. Listening to a radio station, they told users to download their app "on google play or the apple app store". No mention of Microsoft's store. And then later on, I got my Trackr Bravo device and it doesn't support Microsoft either. With iOS and Android, you don't have to worry. Everything important is available for both. With Windows Phone, you need to check what's available. And that's why the phones are so cheap: there are no apps.
No doubt I'll get downvoted because some Microsoft phone fanatic will get upset but that's not my intention. It's just the state of the computer/phone industry. If you don't understand how the market works, and you buy some cheap device, you might get burnt.