You can't force people to release an app, but you can incent them. Conduct market research to find out which missing services are the blocking factors for people to switch. Then approach those companies and guarantee a minimum revenue from WP. If the app makes less, Microsoft will make up the difference. Lend Microsoft engineers to those companies. Or contract it out and have Microsoft pay the bill. Or let Microsoft use public APIs to build third-party apps for those services. Don't take a 30% cut of the money users pay, temporarily.

There were many things Microsoft could do, but it seems they weren't fully committed to the platform.