In describing the the corruption of man, why focus on “every imagination of the thoughts of his heart” (Gen 6:5)? Why not focus on evil actions?

The word translated “imagination” is rendered “intent” by the NASB and “inclination” by the NIV; the Hebrew יֵצֶר, yetser, is glossed “a form, framing, purpose.” In any case, we are speaking of the intentions out of which actions begin. God could see into men’s thoughts, and they matter greatly in the OT and NT alike. One of the deep and easy-to-miss themes of the Bible is the crucial importance of having the right beliefs and attitudes; foolish and vicious thoughts are often said to result in evil acts, and even the Ten Commandments has a law governing emotions and motives (the tenth, concerning envy). Considering all this, the reason for the focus on the “imagination of the thoughts of his heart” must be theological: motives and imaginations and thoughts are every bit as significant as acts, for a spiritual creator. Ultimately, the true corruption of mankind was the corruption of his heart.