Choosing Forth isn't simply an affectation, it has some desirable technical properties:

> Forth is, to my knowledge, the most compact language allowing high level constructs. It is so compact that Collapse OS' Forth implementation achieves self-hosting with about the same amount of resources than its assembler counterpart!

https://collapseos.org/forth.html

https://news.ycombinator.com/item?id=23450287