Another interpretation: It was said only against the generation of the dispersion. (Psalms 59:12 [11]:) "Do not kill them" by the killing with which You killed the generation of the flood. Rather (ibid.:) "make them wander by Your power", toss them about among the people. As it is said (Genesis 11:8): "And the LORD scattered them." (Psalms 59:13 [12]:) "The sin of their mouth", that they sinned with their mouth. "The word of their lips", that they sinned with their lips. Therefore (ibid.:) "let them be caught in their pride." (As it is said.)
Why God Scattered the Generation of Babel Instead of Killing Them
Midrash Tanchuma Buber, Noach 23:2
ד"א לא אמרו אלא כנגד דור הפלגה, אל תהרגם בהריגה שהרגת דור המבול, אלא הניעמו בחילך, טלטלם בעם, שנאמר ויפץ ה' אותם (בראשית יא ח). חטאת פימו שחטאו בפיהם, דבר שפתיו שחטאו בשפתותיהם, לפיכך ילכדו בגאונם. (שנאמר)