This could either mean that Windows 10 has become more secure than its most popular competitors, or that researchers hadn't invested enough resources to audit Windows 10 properly.
Taking into account the results from previous years and previous versions (like 8.1), my personal conclusion is that Windows has actually become more secure.
[1] https://www.cvedetails.com/top-50-products.php?year=2016
The stark contrast is in the privilege escalation vulnerabilities from the Windows side vs the other categories on the Linux side.
I would assume that many persons prefer a server to go down, corrupt its data and leak it, rather than get compromised. The fine print is that the leaked data may contain information to compromise the server[1].
OSX is right behind it, with a culture of laxness that undoes most of the benefits the designers tried to give them.
Not quite as bad, but still pretty weak.