It looked like a risky dependency, simple as that. Despite the HN title, the point of the article was not to talk about React Router.

EDIT: Additionally, I'm not saying React Router is bad per se, just that it's not fully baked. I'm glad to see people working on the problem. I look forward to leveraging the fruits of their labor in the future (in fact, I already do - I use the history library on which RR is built).