Bottom Line (both literally and figuratively)
Why does it always have to be a government conspiracy with you.
I'll give you a reason that a "fat tax" won't work: Some people are 'fat' simply because of genetics or other factors beyond their control. They'd have one hell of a lawsuit if the gov't decided to implement an arbitrary tax on their size or weight.
And by the way, you seem to forget that our representatives pay the same taxes we do. So yes, there are many politicians who don't like certain taxes, for a variety of reasons.