"debugger vendors in 2047 distributed numbered copies only, and only to officially licensed and bonded programmers." - Richard Stallman, The Right to Read, 1997
I only have Linux PCs (laptops) and servers, 100% of my work and personal stuff is done there (though for work I do need to hop into MS365, Google Workspace, Zoom, etc, hooray for browsers, my final firewall between me and the walled gardens, though we can have a whole discussion on that).
For mobile, we have PostmarketOS, Phosh, Ubuntu Touch. I really must try living in them, is it on me? IDK, our government even has an identity app for iOS and Android. I should not be using it, I should stick to web. But its so much more convenient. I'm just weak, aren't I?
Maybe I should go for Ubuntu touch, with an iPad on the side or something. At least my most personal device is something I control then. Or just keep my Linux laptop handy (or make a cyberdeck!). But I want a computing platform that does not require carrying a bag. It's kinda sad. Even GrapheneOS (one of the most personal and secure mobile computing experiences out there)'s future is in the hands of its greatest adversary, the one that does not want you to have a personal computing experience.
Of course, the problem for MS was that Apple (and Google) quickly closed those gaps, and they just simply had better overall products.
But that wasn't the problem.
The iPhone and Android became popular because they were, respectively, good and "good enough" but free, and both Apple and Google had a good reputation at the time. Users were willing to buy those phones and developers were willing to make apps for them because they didn't expect those companies to screw them. The screwing only happened after they were no longer the underdogs and the network effect was already established.
Microsoft doesn't cast as an underdog and everybody expects them to screw you as soon as they get the chance, so not enough people were willing to give them the chance.
They could have overcome that to their own benefit if they would have bound their future selves from enshittifying the platform. Don't make "Windows Phone" under a proprietary license, make an actually open source Android fork which is an open platform like Windows instead of a closed one like iOS, but provide seamless integrations with the Microsoft cloud services instead of the Google ones. Write code that makes it work as well with Windows PCs as iPhones do with macOS. Make two phones yourself: a $999 Surface Phone with iPhone-quality hardware and a $199 one with basic hardware but nevertheless 12 years of security updates to get the low end of the market, provide something for kids/students and make it cheap for developers on the fence to get a device with your platform and make apps that integrate with your cloud services. You're not trying to sell an operating system, you're trying to take Apple's margins on the high end hardware and Google's cloud services revenue from the mass market.
But that's not what they did, and getting people to trust them with a closed platform wasn't in the cards.
Apple and Google might have had a good reputation with consumers who were using feature-phones at the time... but they both had bad reputations with most existing smartphone users at the time. Those users were primarily business business users or power users who had requirements that weren't met by most of anything that Apple or Google was putting out at the time. RIM and Microsoft were building the smartphones that were most trusted at the time.
The mass consumer market for smartphones really didn't exist until Apple took phones in that direction. Before that, they weren't entertainment or consumer-focused devices, they were productivity devices.
iOS and Android, by their second or third release, were already better products than Windows mobile 6.5, both for entertainment and productivity. That's the reason they won. Neither of them were "free" to users -- and in fact the devices that they ran on were more expensive than Windows Mobile devices. People were only willing to pay more for these devices because they were doing something entirely different than what Windows Mobile did. They were consumer smartphone devices -- a new category of device that didn't exist.
This is not to be confused with Windows Phone -- which failed because it was way too late to market, way too far behind in ecosystem support, and didn't solve any new problems.