Back in 2010, Android was still very clunky and sluggish. Windows Phone was sleek and fast. Both OSes allowed you to install developer tools and write software for free.
However, there's 2 differences that no one calls out! First, Android used Java as a way to leverage 15 years of software. Windows Phone v1 was c# only and back in 2010 no one except Stack Overflow was writing anything other than enterprise software in C#. So you literally had to write 95% of your software from the ground up.
Second, instead of quickly catching up, feature for feature with Apple and Android, only 2 years behind at the start, they stopped, not once, but two times to re-write their Phone OS still using the original feature set from 2010.
They should have 1, BENT over BACKWARDS to get every API they could and ship C++ and Java compilers. Talk to developers about what they needed to get their software written. In 2010 and 2011 there were hundreds of developers at every company that would have loved a small 20% project to bring up their software on a Windows Phone. Yet with it only allowing C#, it would have required developers 80% of their time and that was just not a reality.
Second, they should have continually added features and more features, and innovated on features that no one else had. 2010 still had a lot of room for owning the narrative of what a mobile device could be.
I don't know about you, but it frustrates me that they don't own up to their actual mistakes. It's not about the lack of companies building the apps, it's that whoever managed that Phone project was incompetent and mismanaged the whole thing. They treated it like just another 9 to 5 job with little expressed passion for winning.