Because you can't destroy and ideology or the will of a human being. People can try and persuade, but when a group goes up front and starts angerly trying to stop someone from doing something, obviously the person who is being told to stop will retaliate. Fast food will stay the same way it is, because of it's convenience and taste. People have to understand that the people pushing for a healthy diet, are a vocal minority, not a major push. You may hear about this stuff in a school, or get laughed at by some of your crazy friends. I mean look at our drug problem, that stuff is on the rise as well, because the more you protest it, the more it gets stuck in people's minds, and people follow that.
They are flexible, growing larger and larger and making more income every year. Fast food chains are popping up everywhere, and even though the market share is becoming smaller and smaller for each company, the actual market is on a very steady incline in popularity, so no, they are not on a incline