But how many overweight people are just eating too much

How do you determine what is "too much"? If you measure it by weigh gain, then all of them are eating too much. But if you measure it by "they eat until they are satisfied and no more than that", probably most of them aren't eating too much.

and don‘t exercise a lot or at all?

That I suspect is very common. Then again, many modern jobs involve sitting all day and the day has a finite number of hours, and at least in North America cities are car-dependent so many people don't even get to commute by foot. It's an environment that produces very sedentary people.

There is also lack of sleep, which I personally suffer from. How many of us are getting a good eight hours of good quality sleep every night?

There is more to it than "personal responsibility".