I think one of the reasons that Lua gets less attention (outside of certain niches, most notably the game industry) is that, to get the most out of it, you need experience with C or C++. The libraries available for standalone Lua are somewhat small compared to (say) Python, because in most cases you'd just use C libraries anyway. In exchange, though, you can leave each layer to focus on what it does best.

This probably rules it out for people who only know Python, Ruby, PHP, etc., which in turn limits exposure among web developers, who seem to have disproportionate presence on blogs.