Tosfos asks: if Rashi is right, the gemara could have chosen any pasuk that simply lists names. Why these in particular? Tosfos therefore suggests that the pasuk of Ataros v’Divon was chosed because there is a Targum Yerushalmi on the pasuk. Even though this targum is not the “standard” targum of Onkelus, it is still better than just reading the mikra three times.
I saw this year that Rabeinu Bachyei offers a different answer. Rashi 32:38 writes with respect to the cities of Nevo and Ba’al Me’on that these names were associated with idolatry. When the cities were conquered by Reuvain, they changed the names to something else. Rabeinu Bachyei extends this idea to the names of all nine cities mentioned, including Ataros and Divon. One might have thought that since reading the targum here involves reciting names of avodah zarah it should be omitted; therefore, the gemara stresses that even here there is a chiyuv to read shenayim mikra v’echad targum.