My own machine came from OEM with 8.1, but I upgraded during the free phase and while I personally like 10 even more, am sure there are people who are hoping to remain on 8.1 for as long as possible, so it would have been munificent of MS to have supported Office 19 on their platform, but I guess they won't and that's that.
Thats more like a Windows 10 build increase than a service pack. Update 1 uses the in place upgrade method to reinstall Windows. If you dont have Update 1 (which should have been called 8.2) you shouldnt expect software to target your environment.
I would assume the same people who liked 7 better than 10 and wanted to stick with it, and for the same reasons.
For users Win 8.1 was basically a better 7, even though it didn't have any chance from recovering from the (deserved) critics against 8, namely "why did you put tablet minded stuff like that tile screen on my desktop OS, and where is the start menu". 8.1 fixed those issues, and was really "win 7, only better.
> Isn't it pretty much universally regarded as a dud release?
Yes and no, 8 overall is regarded as a dud, mostly because of the "here's the new windows 8, oh wait no we didn't mean it here is the real one named 8.1".
> It seems like the smarter move here would be to kill the LTS for 8 than devote a bunch of effort to supporting their most popular product on their least popular platform.
For a company that makes the majority of their money from b2b I wouldn't call "kill the LTS of a major version of your major product after you sold it" a smart move.