I can't tell where the sarcasm starts and the misinformation stops. Either you don't know your software history, or this entire post is just way too much eye-roll-sarcasm for me to care about interpreting.
Just in case you are not aware, Microsoft released their mobile software platform way back in 2000. This is obviously before Apple or Google entered the space.
The issue that Microsoft faced was not their size but, as normal with them, their execution. Size guarantees nothing. Good ideas guarantee nothing. What matters is the perfect storm of an idea, opportunity, but above all other EXECUTION. People didn't develop for them, myself included, because the platform sucked. It was riddled with issues and device compatibility issues. People used to complain about Android back in the day but it was NOTHING compared to Windows Mobile. Their reboot of it was not much better. At the time I was helping a very successful application group and Microsoft literally paid us to make a version and we finally gave up due to all of the issues we had with getting it stable on a variety of devices.
Also, none of this has anything to do with the fact that applications that run on platforms have great flexibility and choice than do the founders of those platforms. Again, this is not chicken or egg. Platforms take risk and either it pays off or it does not.