Windows NT started supporting unicode before UTF-8 was invented, back when Unicode was fundamentally 16-bit.
As a result, in Microsoft world, WCHAR meant "supports unicode" and CHAR meant "doesn't support unicode yet".
By the way, UTF-16 also didn't exist yet: Windows started with UCS-2. Though I think the name "UCS-2" also didn't exist yet -- AFAIK that name was only introduced in Unicode 2.0 together with UCS-4/UTF-32 and UTF-16 -- in Unicode 1.0, the 16-bit encoding was just called "Unicode" as there were no other encodings of unicode.
By the way, UTF-16 also didn't exist yet: Windows started with UCS-2. Though I think the name "UCS-2" also didn't exist yet -- AFAIK that name was only introduced in Unicode 2.0 together with UCS-4/UTF-32 and UTF-16 -- in Unicode 1.0, the 16-bit encoding was just called "Unicode" as there were no other encodings of unicode.