The idea is that facebook has added stories to facebook, instagram, whatsapp and facebook messenger in a frenetic binge presumable attempt to crush snapchat.
The FB and Messenger ones are different too!? At least the other three are separate accounts, so that's justifiable, but FB and Messenger are the same account, they're even the same website on desktop.
Some would say Facebook/Zuckerberg has gone too far in copying competitors' features into Instagram/Faceboook. Snapchat's Stories is a recent example of this. Hence Zuck.js
Well Zuckerberg is the new Bill Gates. Embrace, Extend & Extinguish. They're on a frenzy to kill snapchat before it gets big like they did with Google+.