I always find it amusing when people slag off big fast food joints.
The very fact they are so successful means most people don't agree with you.
As for the quality of the food. Whilst it might not be the healthiest if eaten often, there is no way people would go back time and time again if it was "shit".
Take McDonalds beef burgers. I constantly see posts on how "shit" they are.
While they might not be to everybody's "taste", the actual meat quality is actually the very best.
Before you think i'm a fanboy, i rarely buy anything from them other than their sausage McMuffins every now and then. If push comes to shove burger wise, i prefer Burger King or Five Guys.
The reason i know so much about their meat is that i have done a lot of research. I've always been into home BBQing, so already have a keen interest. I mainly grind and cook my own burgers. I'm also researching for an upcoming business venture.
I know they buy two cuts of meat that are sold exclusively to them. It gives the burgers a certain taste and texture. It isn't pumped full of anything. It really is only seasoned with salt/pepper. The fat is there to gave taste.
If you ever bothered to eat a plain Pattie from all the main burger joints, you would be surprised how tasty and juicy they are in comparison.
I do think they then ruin them with the toppings and the type of bun. But that's down to personal preference not the quality.