It is true that LuaJIT is stuck at 5.1, but you could write any performance critical sections in C/C++ and call it from Lua.
Lack of LuaJIT for 5.1+ isn't that big of a deal for desktop apps. The embedded world is still stuck in 5.1, but for them, the benefits of the latest Lua is marginal.
And despite it being stuck at 5.1, it still implements features from other versions. For example, there is the "LJ_52" macro, so you can compile "table.pack" and "table.unpack" into LuaJIT, which I do, because I use both at times.
As someone else have pointed it out, they are cherry picked: https://luajit.org/extensions.html.
There is also the compat53 library which polyfills most of the missing parts. The Teal compiler has --gen-target and --gen-compat flags which adapts the generated Lua code for different Lua versions, and allows using the compat53 library behind the scenes if desired, so you can get a mostly Lua-5.3+ experience over LuaJIT using Teal.
and if you use luajit ffi, those calls actually get called just as fast as from a c program