Honest:
Oh wouldn't it be nice if we could reduce the complexities of life to a 30 second sound bite.
It turns out to be more complex than you believe. Eating carbs and snacking frequently results in some physiologic processes that complicate things. In its simplest form (and this is just just touching the complexity) too many carbs raises insulin, promoting calorie storage and most importantly blocks hormone sensitive lipase. This last step prevents the body from utilizing fat stores. 
So our current recommended dietary pattern encourages fat deposition, and prevents it from being reduced.  Not simply calories in calories out. The laws of thermodynamics hold true, but in the context of our hormonal milieu.
Ketogenic diet and fasting fixes the hormonal problem.