My guess is that they preferred bigger optimizations first, such as the given examples of reusing Ryu's body tiles for Ken and mirroring Sagat's legs. If those

My guess is that they preferred bigger optimizations first, such as the given examples of reusing Ryu's body tiles for Ken and mirroring Sagat's legs. If those hit the target, there's no need to go around trying to pick up a tile here and there around the edges. Also, any given saved tile might not have packed well in the overall sprite sheet, given that they were organizing the ROM by hand.