It's widely regarded as a highly performant and very well-engineered runtime for a popular language. For a long time it was the go-to implementation you would reach for if you a) wanted lua scripting (common in game development) and b) wanted high performance.
I think nowadays though, the landscape has changed quite a bit since when luajit was at its peak of popularity.
a) Lua is not necessarily the language one would always choose for scripting, in the first place. There's lots and lots of scripting languages to choose from these days. (It's also increasingly common nowadays for indie gamedev to happen entirely within a game editor, like Unity or Unreal, which provide their own scripting systems. That fact alone has killed a lot of interest in lua.)
b) If you do want to use lua, the features of the official implementation have progressed a lot since v5.1 (which luajit is pinned to), and its performance has improved over the years.
c) There are other competing lua and lua-adjacent implementations to consider as well, like OpenResty's luajit2 or Roblox's Luau.
I think nowadays though, the landscape has changed quite a bit since when luajit was at its peak of popularity.
a) Lua is not necessarily the language one would always choose for scripting, in the first place. There's lots and lots of scripting languages to choose from these days. (It's also increasingly common nowadays for indie gamedev to happen entirely within a game editor, like Unity or Unreal, which provide their own scripting systems. That fact alone has killed a lot of interest in lua.)
b) If you do want to use lua, the features of the official implementation have progressed a lot since v5.1 (which luajit is pinned to), and its performance has improved over the years.
c) There are other competing lua and lua-adjacent implementations to consider as well, like OpenResty's luajit2 or Roblox's Luau.