Sometimes I think it's best for a developer to take a chance instead of playing it safe because it can bring a greater reward. They chose a platform they enjoyed and which they could get in on the ground floor. As they say, fortune favors the bold.
As an example, if The Omni Group decided to go to Windows instead of NeXTStep, there's a possibility that they would never be successful as they are now.
Explains why they tried, doesn't explain why they are sticking to it, unless they imagine the story, both in terms of market penetration and developer support, is going to get considerably better.
Many analysts believe that WP will see more success which is where it starts (with consumer interest). Many devs put up with Apple's flawed and constantly evolving policies because they believe there is financial success waiting on the other side which isn't entirely untrue.
the Windows Phone platform is going through some churn. With the new Windows 8, apps can share the marketplace so you can target the Windows installed base with your apps too. If you have already spent efforts developing the app, leaving it there seems worth it.
Unless you build an app optimized for small form-factor mobile touchscreen devices, in which case much of the same Windows installed base will find it more convenient to use on their Android and Apple smartphones.
As an example, if The Omni Group decided to go to Windows instead of NeXTStep, there's a possibility that they would never be successful as they are now.