The only way out
Only a law or a rule for obligatory publishing of all results (and maybe the establishment of a special journal for negative results) could bring certainty about the reasons for not publishing. And no one would have to think about the reasons behind.
On the other side, the published negative results could help other scientific groups in decision-making when they want to start a new study -- maybe a study that has already failed in the hands of others.
Competing interests: No competing interests