Why are written Khalkha and Buryat more different than their spoken dialects?

Written Khalkha and Buryat appear more distinct than their spoken counterparts primarily due to divergent spelling conventions and differences in vocabulary. While the spoken dialects of Khalkha, Buryat, and Mongol are closely related and exhibit a high degree of mutual intelligibility, their written forms have been shaped by separate political and cultural histories.12

These differences are reinforced by the use of distinct literary standards and the adoption of specific vocabulary—such as the inclusion of Russified terms in Buryat—which are reflected in their respective Cyrillic writing systems. Consequently, the written languages do not mirror the close proximity of the spoken dialects, which remain little differentiated apart from vocabulary.21