Why did Scottish Gaelic become a separate written language from Irish during the 17th and 18th centuries?

Scottish Gaelic emerged as a distinct written language during the 17th and 18th centuries primarily because the previously shared literary standard, Classical Modern Irish, became increasingly inaccessible and foreign to Scottish speakers.12

For centuries, Ireland and Scotland utilized a common Gaelic literary norm. However, as the Scottish Reformers attempted to use the Irish Bible, it became evident that the language was too foreign for the local population to understand. Consequently, a native Scottish standard began to emerge during the 17th century as poets who were unfamiliar with the Irish norm started composing works in their own regional dialects.21

This transition was solidified in the 18th century when the orthography of Scottish Gaelic became more fixed. While manuscripts in a distinctively Scottish form of Gaelic had appeared as early as the 16th century, the shift away from the Irish literary norm was driven by the practical need for a vernacular that reflected the spoken language of the Scottish people.12