Because what good can come from discussing that topic? The only reasons to broach it are to a.) troll and/or b.) agitate for some horrific policy proposals.

He's not an academic researcher. Don't you think it's odd for some old white guy to get worked up over minority test scores? Why write about this rather than basically anything else? Either he's a troll or profoundly unaware about how bringing this line of argument up may make people feel threatened. There are a lot of things that simply don't need to be discussed. It's like graphically describing your partner's episiotomy over dinner. Some things just inspire a visceral reaction.