Maybe to target retro computers and systems?

Right at the very top of the article:

> Let me tell you the story so far; the process, obstacles, and solutions involved in making a roguelike dungeon crawler playable on systems like the Commodore 64, Commodore PET, and even more constrained machines.

Javascript is not running on a Commodore 64 with decent performance.

These are machines where having 64 KB was already great, many had 16 or 8 KB!