The real issue is that we seem to be purging all the wrong things.
Useful answer to technical question? Gone five years later.
Unfounded and fraudulent accusation that some teenager in Albuquerque committed a hideous crime? Preserved for the ages. Revenge porn photos? Also preserved, although possibly without the attributions.
Although, really, all of that is human nature too: we conserve what draws the attention of the average mook, not what specialists find useful.