The addition of Unicode support to Windows NT was probably done a great deal in advance of its actual release--it's not the sort of thing you can throw in the last minute.
It's also worth noting that dealing with UTF-8 correctly is more than just declaring "the encoding of this set of characters is UTF-8"--it does require you rethink how string APIs are designed to work well. If the alternative is a 16-bit fixed-with character format, UTF-8's variable-width format doesn't necessarily look like a wiser idea. It's not until 1996, when Unicode moves from 16-bits to 25-bits, that UTF-8 actually looks like a good thing.
It's also worth noting that dealing with UTF-8 correctly is more than just declaring "the encoding of this set of characters is UTF-8"--it does require you rethink how string APIs are designed to work well. If the alternative is a 16-bit fixed-with character format, UTF-8's variable-width format doesn't necessarily look like a wiser idea. It's not until 1996, when Unicode moves from 16-bits to 25-bits, that UTF-8 actually looks like a good thing.