The character for this word intuitively hints at its meaning, consisting of the meaning-element enclosure ⼞ and the sound-element 化. Other than that, this character won’t help us discovering the origin of the actual Japanese word otori.
There is, however, an alternate spelling of the word: 媒鳥. Well, the first character is questionable, but the second character tori, bird, gives us a valuable hint regarding the etymology. So far, so good. Now comes the moment we need to consult a dictionary, and we discover the last piece of the puzzle.
The current word is contraction of oki-tori. Tori mean bird and oki is and old version of the verb maneku which means invite, call for. The whole phrase otori thus literally translates to inviting bird. And in fact, otori originally referred to a bird one would use to attract and catch birds of the same species. Over time, this meaning became extended to humans.
Now you know it. To the Japanese mind, people are like flocking birds. Fits the Japanese sense of community : )