[andrewl-hn]

For many European languages like French or German the switch from local CP-encodings meant that only some characters like å, ñ, ç, etc. would require extra bytes. And thus the switch to UTF-8 was a no-brainer.

On the other hand, Cyrillic and Greek are two examples of short alphabets that allowed combining them with ASCII into a single-byte encoding for countries like Greece, Bulgaria, Russia, etc. For those locations switching to UTF-8 meant that you need extra bytes for all characters in a local language, and thus higher storage, memory, and bandwidth requirements for all computing. So, non-Unicode encodings stuck there for a lot longer.

[gblargg]

And back then Unicode was just 16 bits so UTF-8 wasn't such an obvious advantage in flexibility.