Microsoft tried hard, and kept trying long after it was clear to most of the market that they didn’t have traction. The owners of Windows phones were some of the most vocal champions at the time too. They legitimately made good but unpopular products at the time.
Wait, what was that about? Microsoft was incapable of building a Windows Phone email client that used OAUTH?
And bear in mind, OAuth to authorize mail access is weird. Generally speaking, mail clients use IMAP or POP3 and SMTP. One of the more popular open source Android mail clients, K-9 mail, still doesn't support it: https://github.com/k9mail/k-9/issues/655
But the biggest issue is that, like the "unknown sources" checkbox in Android, Google uses scare tactics to discourage non-Google-proprietary apps and protocols. Use Google apps on Google devices only, otherwise you'll have to authorize "less secure" things.
Microsoft had WinCE then Windows Mobile for quite a few years before the iPhone, then Apple released the iPhone, Windows Mobile started hemorrhaging market share... so Microsoft dropped WinMo like a bad habit, leaving developers and users out in the cold. STRIKE 1
Windows Phone 7 came out with piles of great press and hoopla, but notably, it didn't support older hardware so existing owners were left in the lurch. Developers were also screwed because WinPho7 wasn't compatible with older apps. It was a pretty interface with no software, no users, and no developers. It also had some serious shortcomings, ironically iPhone enterprise support was much better. WinPho didn't work well with Exchange server or Office. But that's OK because you didn't have long to be frustrated with WinPho 7 because 2 years later, they released Windows Phone 8 which dropped support for all old hardware. That's right, if you bought a brand new Windows Phone 1 year after launch, you couldn't run the next major release of the OS.
But the few people who managed to stick around after getting screwed over twice... boy did they love their Windows Phones.
After a certain point, there were just no developers, OEMs, or end users left around willing to be Charlie Brown to Microsoft's Lucy.
Also, for quite some time before they officially pulled the plug on mobile, core MS apps would come out for Android first.
Microsoft really despised their customers.