Calling LuaJIT unmaintained isn't exactly true. It's still getting commits, however the author has stopped trying to keep it up to date with the mainline Lua updates. Lua has a history of not caring too much about backwards comparability, so the LuaJIT devs have decided to stay with Lua 5.1, even though 5.1 is nearly 10 years old, and 5.4 is on the way soon.