I might be missing something (after reading the article twice) but the author says nothing about why he doesn't use React Router...

The only mention I can find is "But the API smelled funny to me, and had not settled, so I continued to wait" that hints that the API is changing and looks weird. But other than that, there is no constructive criticism here.

I'm all for being able to write freely about software we find bad, but without any concrete examples or even pointers to what is bad, I don't think this article have any merit (except that it's good to make sure you understand the dependencies you have).