Seriously? Are you sure they are worst "wasters" of energy on the planet right now? What about cars, and eating meat, and Christmas lights, and so on? Have you checked your own energy consumption today?
It seems to work well enough for at least some use cases, no matter how low the number of transactions. Further developments like Lightning Network are being worked on to enable other use cases.
I don't like if they burn coal for it, but there are also other energy sources, sometimes there is even spare energy that needs to be used somehow.