I'm not convinced by that. If Maemo was a natural fit then Microsoft surely was equally so, given they already had Windows Mobile. They also had a large army of developers familiar with Microsoft APIs and the financial backing a large tech company can provide (IIRC MS literally paid people to make apps for Windows Phone). That's the kind of thing you'd need to catch up in an app library race you're already losing.

Yeah, we can look back in retrospect and say it was an obvious failure but that's because of the various insane choices MS made over the years. In the moment I'd argue the decision was nowhere near as clear cut.

They had no developers familiar with these Microsoft APIs as Windows Phone was starting from scratch with new APIs that were incompatible with neither Win32 nor Windows Mobile. The only thing that could save them that they were betting on was that these new APIs were also made available on desktops, but were pretty much ignored by developers there as well and ended up largely replaced with an even newer set of technologies.

Compare that with Maemo, where both GTK+ and Qt were first class citizens and which had an army of developers familiar with Unix and X11 before Maemo even existed.