Because nothing good can come of that.
If we have decided something, it is not very objective, is it? There is a difference between truth and consensus.
Collecting information (which is public by the way) is just yet another hobby, which can be used for good (training an ML algorithm), bad (annoying someone), or just be neutral (sitting in someone's archive). It does not mean that you use it to ruin someone's life.
Also, there is nothing wrong with stalking people, as long as you do not interact with them, let them know, or affect them in any way.