The problem is that pretty much nobody used Windows 8 on anything other than desktop/laptop devices. Microsoft had to start building their own tablets to push

The problem is that pretty much nobody used Windows 8 on anything other than desktop/laptop devices. Microsoft had to start building their own tablets to push other manufacturers to build Windows tablets, too. They literally had to buy the only company making Windows phones exclusively to ensure that somebody makes Windows phones (even though nobody seems to want to buy them).