Because McDonald's is the giant. There's one every 5 minutes walking distance in London. It's in every country; it supports the Olympics along with Coca Cola and Cadbury's which is a complete contradiction seeing as the Olympics is about sport and being healthy. I know you could argue "But KFC and Burger King are also in different countries" - McDonald's is a global brand like Coca Cola.
A McDonald's salad has just has much calories as 1 McDonald's burger, because of the dressing; and most people see going to McDonald's for a salad is like going to a prostitute for a hug. I personally don't eat at McDonald's; their chips are way too salty which is another thing the media moan about; why can't we have separate salt sachet's and put our own salt on? I eat at Subways and sometimes Burger King if I feel naughty, because their chips are plain.
If you're talking about American School's; yes you have a problem, over here in the UK we don't have the problem so much anymore thanks to a chef called Jamie Oliver. He did his research and explained to parents what really goes into school dinners and some parents blindly didn't realise that their child is having the exact same thing at lunchtime when he/she comes home from school to have dinner.
http://www.youtube.com/watch?v=P-mYAoWu-O8