Processed foods are a vaguely defined and somewhat arbitrary category of foods, but that does not mean the correlation between foods being highly processed and unhealthy is BS. Things that have ingredients like brominated vegetable oil or various other preservatives and stabilizers for texture and shelf life, artificial colors and lots of HFCS, meat slurries that have been pumped through tubes and formed into precise shapes, the "simulated yogurt" that wrapped the raisins in my trail mix... None of that stuff is a favor to your health.

Food optimized for mass market scale and profitability is practically never optimized for nutritional value, except as a hollow gimmick, e.g. Vitamin Water.