In my case it’s because forth is one of the only high-level languages that has a chance of running at a playable speed on the NES, and I just like the language in general.

If you look at old school development manuals for stuff like the C64 your options, to get decent performance for something you are writing it seems like the options were “forth” or “assembly”, and I find forth easier to reason about.

To answer the true essence of your question though, I wanted a forth compiler as a means to making an NES game, but after I got Codex to generate the compiler I kind of realize that what I actually wanted was the entire experience of making an NES game, including building the compiler.