One of the reasons is because they used the switch to ARM to lock the system down tightly. Mandatory secureboot that couldn't be disabled. A Windows system that's not as open to modification as the x64 version.

They did their level best to get maximum control and this was and is a huge turn off. If they made it as open as x86/x64, and pulled out all the stops to get software support equivalent to x86 like Apple have done with their system, then it would be a compelling proposition. As it is, it has woeful software support, and Microsoft did very little to address this.