Several verses in the books of Devarim (3:4-5, 14) and Yehoshua () speak of as many as sixty (!) cities included in Yair's territory. Why then does the Torah speak only of villages conquered by and named for Yair?
A few verses earlier, the Torah mentions that Bnei Yisrael renamed cities which were previously named for idols and idolatry. The commentaries (see Rabbeinu Bechaye) explain that this was in fact the motive of the tribes who asked to settle in the lush lands of Sichon and Og: to prevent these agriculturally attractive areas from being repopulated by idol-worshippers who would dedicate these cities to pagan deities once again. Instead, the tribes of Reuven, Gad and Menasheh capitalized on the opportunity to occupy these cities with service of G-d, and to annul the idolatry which previously occupied this space by changing its name and identity.
By referring to the areas that Yair conquered as villages, the Torah alludes to this transformation. Chazal (see Chagigah 13b, Rashi ad loc.) contrast the reaction of one who lives in a metropolis or capital city upon seeing the king, with the way a villager reacts and reports it. For the urbanite, the king and his entourage are a common sight. For the villager who is unfamiliar with seeing royalty, this is exciting and novel.
Therefore, the Torah emphasizes that Yair conquered “villages” and called them “Villages of Yair”. For Yair’s line of work was marked by the villager-like constant excitement of the King of Kings making His appearance in places where until then He was relatively unknown.
—Likutei Sichos vol. 38, pp. 120-121