Or it's just incentives: if they rule the case is a suicide, it's closed and they can move on with their lives, while if they rule it's a homicide, it opens up a whole criminal investigation and media circus, they'll have a lot of attention on them, they'll have to testify at the trial, there are potential career repercussions if they're wrong (i.e. no conviction), there are potential personal repercussions if they're right and various powerful people would like to see that fact buried, etc. If there's any ambiguity at all, better just lie low and go with the conclusion that means the least work and risk.

HN tends to attract people who believe in finding the Truth with a capital T, but the majority of the world does not function like that. Most people are more concerned about personal costs and benefits and how a given action will affect them. The abstract Truth out there is immaterial; they just don't care, and save their energy for things that matter more to them. Explains a lot about the media, politics, corporate scandals, and so on.