Why are so many people fat and obese?

I grew up a fat kid, I lived on McDonalds and such. Then around 18 I decided to take action as I knew my body was not the way it should have looked at that time.

I see photos of my friends and family on Facebook and they are all getting to a point they look unhealthy? I get it some people are born with different body types however staying active and eating right is not that hard to do. So why are soo many people getting fat?

Do you think exercising or having people see you being active is helping them to get their own weight under control. Or do they see an athelete and say, nope thats not for me.