It's also a very old embeddable language, which is probably most of why it's so often chosen for that purpose. Many similar languages have been written from scratch inspired by Lua over the last 10-15 years, some of them almost definitely better than Lua in many respects, but they get no traction because Lua has all the steam. Unfortunate, because the authors of Lua are fairly happy with semantic and syntactic decisions that many of us are very unhappy with.

Or the number of routers that are using it, or other deployable hardware...