I used to feel the same way you guys do. I used to think that overweight people just needed to eat less, exercise more. Lazy people just needed to get off their asses and do something. Alcoholics just needed to not drink. Drug addicts needed to just stop taking drugs. Pretty simple stuff, really. Right?
Wrong.
I just typed up a full page about having ADHD and how a combination of luck and the correct medicine has changed my life, and my family's lives for the better, but meh... It didn't translate as well as I had hoped. The fact is, my brain is wired differently than other peoples. Just like yours is different than mine, your boss, your neighbor, etc. Different chemicals in my brain work differently than certain chemicals do in your brain, and vise versa. When those chemicals are out of balance, it becomes much harder, and often times, near impossible to reach the goals or whatever you're trying to reach by yourself. If you've never struggled with weight problems, depression, addiction, or any inner demons, then you're lucky (and probably full of ****), but for the rest of us, we have to figure out how to deal with them. Some people can just quit smoking cold turkey, and it works. Some people can just wake up one day and say, "I'm going to the gym five days a week until I'm not fat anymore" and they do it. Some people realize that drugs are killing them and they stop. Most people don't make it when they "quit cold turkey". Most people stop going to the gym after the 1st week in January. Most people stay hooked on drugs.
Why is it that some people can and some can't? I smoked like a chimney for five years and quit cold turkey. It was the easiest thing I've ever done. I don't understand why more people can't do it. On the flip side, getting out of bed when my alarm went off in the morning was pretty much the hardest thing on the planet for me to do; even if it meant I'd lose my job, be suspended from school, or my dad would beat the **** out of me. I failed at that aspect of my life for 20+ years. That is, until I figured out what the problem was, got the chemicals in my brain back on track, and started on the path to recovery. Thank the stars that my issues were easily solved. People who struggle with drug, alcohol, and other addictions don't have it so easy. There is no miracle pill. (yet) People have to struggle with what God gave them, and for some people, it isn't much. I don't know if I would call it a disease, and if you don't like the term, then fine, I can see that. It is a real problem, however, and it's not one that is as simple as "eat less, exercise more". Life in general, both personally and in the world around me, took on a whole new meaning when I finally realized and believed that fact.
tl;dr
It's not as simple as you think. If you can't dunk a basketball, you can't just wake up tomorrow and say, I'm going to dunk this ball because I REALLY WANT TO. The human brain isn't wired like that.