> The Byzantines created the cyrillic alphabet in the 9th century so that they could write a bible for Slavic countries.
A bit similarly: English uses the Latin alphabet mainly because, as I recall, after the fall of Rome the Christian church was doing much of the writing in (England? Wales? British Isles?), and they adapted the Latin alphabet to the local languages.
For a while being literate in Western Europe was the equivalent of being able to write/read Latin. Also almost all the major languages in (somewhat) literate societies in Western Europe were were either dialects of Latin or in much closer contact with Latin countries than the Greek world (e.g. Ireland or Germany, I don't think we have much if any surviving non-Latin texts from Britain until quite late).