The 3:2 aspect ratio probably makes it less consumery as well.
Surfaces (Pro and standard) have been 3:2 for a couple years: https://en.wikipedia.org/wiki/Surface_3
Not refuting your implication necessarily, but worth knowing their flagship (standard and high-end) devices have been 3:2.
I see where you're coming from, but those aren't large screen devices.
Most games and movies are widescreen these days, and I see those as consumery activities. I think a significant amount of consumers would be annoyed by letterboxing in those use cases.
Microsoft has plenty of partners to compete with the iMac. Now those partners can look into the Surface Studio as something to aspire to.