because the slight advertising advantage that you would gain by weight-biasing a can would be completely negated by the huge increase in cost. Even if it costs just one percent more to produce such a can, due to the sheer volume of aluminum can production (on the order of millions daily) the increase in production cost would be tremendous.
Look at a top of a soda can. See how it tapers in toward the top of the can? That allow manufacturers to use less aluminum in the lid, which is the thickest part of the can. The tiny reduction in diameter looks rather insignificant, but it actually saves about 10-15% in the total aluminum required to produce a can, which translates to millions of dollars.
-patchy