Gates plays the long game. The man dodged multiple requests over decades to publish this og code that launched MS as a company (pretended he had misplaced the same or forgot to reply or something): only to perfectly time it for a jubilee release.
I wonder were most of the comments added later? I guess they used pen and paper to write the ASM code and then enter it as machine code.
I imagine that was one of the happiest moments in his life (completing Altair BASIC).