Because Lua is popular among game development enthusiasts? It is THE scripting language of game development. It's the language of choice by Roblox Studio.
I'd say its the language of choice for game modding (which roblox pretty much is) specifically, but not game dev as a whole. In fact I'd go so far as to say its not used in game-dev enough, it seems to be greatly under-appreciated. The only engines I can think that use it are PICO-8 and Love2D.