I guess if you count experimental philosophers like Joshua Greene & Fiery Cushman as metaethicists, then there are a few metaethicists who know some of this stuff. But I was thinking of more traditional armchair metaethicists.

Metaethicists do a wide variety of work. A few have written things worth reading, like Richard Joyce and Stephen Finlay.

Metaethicists discuss a broad range of issues, many of them invoking descriptive claims about human motivation. For example, many of them argue (largely via introspection) that motivational internalism is true in humans. But the recent psychology/neuroscience of human motivation makes this position unlikely to be true, as I'll argue in a future post.