Why do Sakha and Dolgan differ considerably from other Turkic languages?

Sakha and Dolgan differ considerably from mainstream Turkic languages primarily due to their long-term geographic isolation in northeastern Siberia.12

While most Turkic languages are spoken in a nearly continuous band that facilitates mutual intelligibility, the Sakha and Dolgan have been separated from other Turkic-speaking groups for centuries. This isolation allowed the Sakha language to develop distinct, deviant features, even though it maintains an affinity with the northeastern branch of the Turkic family.231

The Dolgan language is closely linked to this development; the Dolgan people, who are of Tungusic origin, adopted a dialect of Sakha after migrating to the Taymyr region in the 18th century. Together, these two languages form the North Siberian group of the Turkic family, distinguished from the rest of the family by their unique linguistic evolution in the Arctic environment.452