Actually atom was very efficient, but they tended to pair it with a horribly inefficient southbridge that would idle at many times the full CPU power draw (2-3W or more)
I had an Atom 330 server, worked really well. It came with came with one little very noisy fan ... on the chipset. The CPU just had a small heatsink. It was okay for my server use case, but the entire situation was pretty silly.
It seems clear Intel was either intentionally trying to hamstring this market or at least trying to make up margin by bundling it with an obsolete process chipset.