While null or negative findings may be suppressed for a variety of reasons (e.g. the assumption that such research isn't "publishable"), industry is perhaps uniquely motivated to conceal unflattering results. Read more below.
There are journals that explicitly welcome and publish articles describing null or negative findings. See the below for examples.
Publication bias is any tendency on the parts of investigators or editors to fail to publish study results on the basis of the direction or strength of the study findings.
Publication bias suggests that negative or null findings often aren't reflected in the scholarly record, which means we don't always have the full picture of a drug's effectiveness or impact, for example. If all we see in the literature are the cases where the drug was successful, we could have a false impression that it is always and only successful. This could be misleading at best, dangerous at worst.
See the videos below for more.