They didn't. As noted in the article, they chose a higher-level platform, found it too limiting, and gradually started just writing code directly for the interm

They didn't. As noted in the article, they chose a higher-level platform, found it too limiting, and gradually started just writing code directly for the intermediate language used. It's similar to putting some inline asm in your C to do things not possible in C, then eventually hitting the point that your entire application is inline asm with no C left.