Who benefits from incompatible batteries?

Following a recent house move, I purchased a number of cordless tools, most of which use 18V battery packs. These are functionally identical, of similar capacity, shape and size, and use very similar cells inside, yet are totally incompatible between manufacturers. As not every manufacturer makes every type of tool, this means I have five different batteries and chargers for five tools, which is not only inconvenient and expensive, but hardly environmentally friendly.

I am unlikely to use a drill, a lawnmower and a vacuum cleaner at the same time, so the ability to share batteries between tools would be extremely useful; three batteries and a single multi-charger would be plenty for my needs, saving money and the environment while leaving me with more spare batteries for each tool than I have now.

Why on earth can’t we have a standard 18V battery pack that fits everything? The double-A battery and its cousins...