I think there's two reasons people might be annoyed with Maurer. 1st is the possibility that he never had an actual drug problem, and he's using this as just a way to get props on social media. Which seems likely because it is difficult (but not impossible) to be a college athlete and maintain a serious drug addiction, JMO.
2nd, as a matter of opinion, I don't think this is the type of thing I would personally share on social media. We all have battles that we face that just shouldn't come with any expectation of personal glory, and this is one of those. Aside from that, Maurer has always failed to understand that is Twitter represents his personal brand, as well as the school. It doesn't do him or the school any favors by discussing his drug issues or sobriety on Twitter and that's par for the course for him. Maybe that isn't fair, but it is what it is.