[beagle3]

Likely for the same reason everyone tries making their own web browser, even though the other guys' are all gratis (and many of them libre): When something is a platform, you are either a landlord or a tenant.

Google and Apple have seen what happens to Microsoft's tenants, so they decided to be landlords. Microsoft knows how awful a landlord it had been (and after decades of landlord-only status, suffered abuse as a tenant at Google's gmail and youtube platforms), so it also tries to be a landlord in every way it can; It couldn't attract it's own tenants to Windows Phone, IE11 and its own Edge, so it has to offer subleases on Android, iOS and Blink(=Edgium) these days.

QUIC looks more "behind the scenes" as a platform right now, but building your own is a very cheap hedge against ceding complete control of what could become a potentially fundamental platform to your competitors. So everyone does that.

I'm no fan of Microsoft, and I believe that Microsoft has been "beaten to submission" rather than "left the dark side", so to speak. But regardless of the overall technical quality or moral/values one assigns to Microsoft - they are a smart, politically and business oriented and savvy corporation. This is a "staying relevant and in control" move.