TCL's good for string stuff, but gets very messy if you want to do stuff outside of that. It wasn't really designed originally as a general language: it works and does have some (IMO 'too') clever features, but it has a lot of foot guns as well: comments are actually (almost) ignored procedures, which causes issues, you sometimes have to escape comments or they'll change logic or cause syntax issues (i.e. trying to comment out statements sometimes still triggers syntax errors within the comment!), everything's a string which is great for strings, but not when you need to start validating numbers or similar... TCL makes a lot more sense as a command language (what it was originally designed for - string commands) or a REPL...

Back in the late 80s before Python and Lua were released the following decades, TCL made sense, as it was the only freely available embedable language.

Python's larger and more complete (and I'd argue a better language then Lua), but Lua's compact and very fast as it's a register-based bytecode VM (and luaJIT exists which is even faster) (although if you don't use the 'local' keyword on variables, it's then quite a bit slower as it no longer uses stack-based variables, so the code can end up being more verbose to make it fast), so games commonly used Lua for scripting/gameplay as it was easy to integrate.