Peter Kirwan, in a great dissection by Wired UK:
Offloading OS development to Microsoft has saved Nokia a substantial amount of money. But doing this only makes sense if you believe that owning an operating system matters a lot less in the mobile realm than it did in the PC industry. Ben Evans believes that what really matters is getting operators to stock your phones and building up apps. “Nokia and Microsoft don’t yet have an app ecosystem,” he explains. “But as a developer, if you come to them from Android, it feels great.”
It’s a hugely complicated issue for Nokia, because they rely on Microsoft to bake the core features into the OS, something with which they have been struggling. Evans is right, though: a fresh ecosystem on a new operating system is exciting for developers, especially if they know they can make money. However, apps on iOS and, to some extent, Android are making money for developers. What’s the incentive to bet on a very small section of the market?