Given how popular smartphones are these days, as well as an important device in our lives, it's not surprising that mobile app software developers are in such high demand. In some places, such as the Silicon Valley region in California, there's a relatively high employee turnover rate in general, due to the supposed lack of skilled mobile developers. It is not unusual for developers to move from company to company within 1-2 years.
Developing mobile apps takes a specialized approach that is not required with regular desktop software or Web apps. Of the handful of different mobile OS (Operating System) platforms available, one of the more popular is Apple's iOS. This mini-course guide to iOS app development should give you a good starting point for learning to develop apps, and monetizing and promoting them. If you're looking for full courses, check out the "Additional References and Resources" section.