The "just" was supposed to apply to the whole self-aggrandizing trip.

My point is that there are a lot of people with math PhDs, but Kun is in a small unenviable minority that is driven to engage in self-promotion via all these blog post "primers", which of very dubious pedagogical quality.

“Oh no, someone is attempting to teach, how dare they!” is what this reads like. Writing articles like this is good for the author, in terms of finding new ways to explain things, and clarify knowledge they already had. The writing style of this author in particular is quite engaging for myself and (I would assume) many others.

I enjoy his content and I have found some of his explanations novel and enlightening.

I don't know why him spending untold hours producing detailed content is a bad thing. Even if it is for self-promotion.