Fenton Sludge tried to keep clean, he really did... but then, the endless lure of toxic profits from his factories once again consumed his soul and led him back to his old ways. As he festered in his opulent squalor, he became obsessed with revenge against that... that Goof who had temporarily led him astray.
"His son! That's how I'll get back at him... yes, a youth internship program at Sludge Industries, with high pay and outlandish benefits... that will draw him in, and then... he will be mine!"
That part didn't work out. Fenton Sludge never lured Max into his nefarious lair, but he did manage to turn Roxanne, Lisa, and Mocha Chino into his new interns, which was probably better in the long run!