I reckon the reputation of Windows 10 as a buggy mess has a lot to with it. I know people who went Mac because of Windows 10 issues. Just recently one of my friends were venting on Facebook about how Windows 10 was slow, annoying and constantly updating and she should have gotten a Macbook instead.
People started getting annoyed with 8 and Microsoft has only made things worse with 10 imo. So much so that MS has to force Windows 10 down people's throats via stealth updates and such. When people don't even want your new Operating System for free you know you've got a problem.
Not to mention OEM and thier shit tier bloatware and McAfee that makes the computer slower than it is.