Google is the web monopolist, and would never build apps like YouTube or Maps for a Windows phone product, since it would compete with Android, and not have the market share of the iphone.

Microsoft tried making their own YouTube app, which Google had taken down. Without access to the Google web products, a new phone ecosystem is going to be dead on arrival

I agree Microsoft flubbed the strategy, same with Zune where they had a technically superior product but no commitment.

Platform reboots killed any developer momentum they built - Windows Phone 8 apps were not backwards compatible with Windows Phone 7 which itself was a clean break with Windows Mobile. A lot of trending apps like Instagram and Snapchat never released apps on the platform, so you had to use third party knock-offs that chased private APIs. Microsoft did build some great social media integrations that tied your contacts into a single local profile across platforms (Foursquare, Twitter, Facebook).

They also kept rebranding and shuffling services on the phones - for example Zune became Xbox Music became Groove.

There were 200K apps in the windows phone store, that would have run on day one when windows 8 released. Instead Sinofsky wanted to kneecap devdiv, and created windows rt API, which was a C++ mess that led to developers completely abandoning the windows platform.

All app development on windows phone stopped when windows rt for windows 8 was announced. Windows phone was miles ahead of Android at that point. In terms of apps they had 200K in comparison to Androids 500-800K apps.