My guess is the danger factor. This guy made his living diving and probably didn't want to push the standards higher for safety. In that sense it is just as good to tie for the world record as it is to break it.
Let's say he dives 173 and lives and then the next guy dives 174 and dies. Basically he pushed that guy to his death when at 172 he along with one other guy get to say the hold the record. If everyone is diving 172 then the record can be pushed higher.