No reason, I suppose. In my opinion it seems to just be a holdover from the previous systems of publishing. The prestige of a journal is ranked based on how often it gets cited (or in other words, how influential the papers are within the journal). Publishing insignificant/uninteresting data would lower a journal’s average citation count, which would make it seem less prestigious than other journals. Hence journals are incentivized to only publish interesting data. It’s a shitty system that everyone knows is shitty but nobody has a good solution for how to fix it