I want to see the exchange as work for time, because I work much more effectively than many other people. An hourly-rate job is simply not attractive to me, because the hourly-rate will not effectively capture my value.
As explained by grellas above, overtime in the US is typically applied to replaceable workers who's hourly value is a more or less quantifiable resource. If I'm flipping burgers, painting a house, or banging out simple webapps based on someone else's design then it's fairly easy to quantify the value of my time.
However, if I'm working in an industry where force multipliers abound, for example software engineering, or any sufficiently advanced executive/management position, I would much rather capture the value of what I produce -- there simply cannot be a good fit with shoehorning me into an hourly value rate. It simply isn't an accurate way to represent my value.
This is best exemplified by jobs which supply equity stakes. If you give me a chunk of your company I'm no longer working for free, when I work overtime.
Why not? If you provide better value per hour than others, you should also get higher hourly rate. If you just work more hours without more compensation, then you're just cheap.