The difference, of course, being that in semigroups we can "fall" inescapably from one J-class to another, but in groups every* element is in the same eggbox (compare transitivity with Boethius and the Wheel of Fortune).
Lagniappe: https://www.youtube.com/watch?v=-yvpRvd44s4&t=90s
* different identities are but a conjugation away?