It’s the nitrates and other preservatives, falling under the ‘processed food’ label.
This should be basic ‘food 101’ knowledge for anyone seeking better health.
Long ago, when I was recovering my health and making that choice to avoid all processed foods, I decided to make hamburgers for the week on my grill for lunch. One day during that week, I had a thought and disassembled the burger - made of 1/3 lb lean ground beef, romaine lettuce, onion, 2 tomato slices and cheese - and put the components in a bowl.
It was a reality check: I’d made a salad on 2 slices of whole grain bread with protein.
No different than a purposeful salad, a burger is only as healthy as what you put on it (same for pizza).
(True story: I lost 55 pounds during my health recovery eating a healthful breakfast, burgers for lunch and pizza for dinner...all homemade but, as I’ve stated prior, ‘eating clean’ is not panacea. It is merely one step of the ‘awakening’ for those who are diseased)
That too, but the dog is healthier because it has fewer calories just kills me.