Why is Ossetic classified as an East Iranian language despite being spoken in the Caucasus?

Ossetic is classified as an East Iranian language because it is the modern descendant of the language spoken by the ancient Alani, a Sarmatian people who were nomadic pastoralists in the steppe region northeast of the Black Sea.12

While the Ossetes reside in the Caucasus, their linguistic classification is based on this historical lineage rather than their current geography. The language preserves archaic features of Old Iranian, such as verbal prefixes and an eight-case system. Although Ossetic is genetically an Iranian language, its development has been significantly shaped by its environment; its phonology has been heavily influenced by non-Indo-European Caucasian languages, and its vocabulary includes a large number of loanwords from Georgian and other regional languages.134