Yep, the almost impenetrable security of the last few Xboxes shows that Microsoft does have it in them to architect a very secure platform, even against physical attacks, but they don't have the luxury of doing such a clean-slate design with Windows. They can almost never afford to break backwards compatibility and the Xbox approach of running each instance of legacy software in its own fully isolated virtual machine wouldn't really scale to a multitasking environment.

For those not keeping score, the Xbox One only recently got a very limited jailbreak a decade after release, that only works on old firmware and only allows access to the innermost level of sandboxing, with the outer system sandbox, hypervisor, bootloader and optical drive handshake remaining unbroken to this day.