C. F. Keil and Franz Delitzsch on Genesis 6:13

Gen 6:13

“The end of all flesh is come before Me.” אל בּוא, when applied to rumours, invariably signifies “to reach the ear” (vid., Gen 18:21; Exo 3:9; Est 9:11); hence לפני בּא in this case cannot mean a me constitutus est (Ges.). קץ, therefore, is not the end in the sense of destruction, but the end (extremity) of depravity or corruption, which leads to destruction. “For the earth has become full of wickedness מפּגיהם,” i.e., proceeding from them, “and I destroy them along with the earth.” Because all flesh had destroyed its way, it should be destroyed with the earth by God. The lex talionis is obvious here.