one of the reasons i guess is on the latest version of lua i believe that they have removed the key word continue for example . and most games use this keyword for their game
Lua 5.1 is a very reliable version which has been used for years and AFAIK Lua v5.4.7. has removed some old features from v5.1. Plus Roblox has removed many functions from debug library from Lua v5.1 or recreated them so people can use it on Roblox.
So in conclusion its just an unnecessary work to implement Lua v5.4.7. to Roblox LuaU because it can bring some bugs, misunderstandings, will probably take a lot of time and problems with compatibility with old places since Lua v5.4.7 removed some functions that was in Lua v5.1.
P.S. According to what ‘xxmanado’ said they removed ‘continue’ so they(Roblox team) will have to recreate it manually.