The issue may be the fact he has a DBA instead of a PhD. I’m not sure I have seen tenure track professors at a Top 25 with a DBA, although I’m sure someone could prove me wrong.
Historically, HBS only offered DBA programs. They renamed the DBA to PhD just a few years ago. Nothing about the program changed, just the name changed from DBA to PhD. Weird, but true. It's a bit different in most other universities I think where the DBA focuses more on applied research.