Because there are only four billion addresses all in all. Every device that wants to be reachable on the Internet needs one. These days, mobile devices don't get a public address anymore and there are all sorts of complications due to it.
We're slowly transitioning to a new scheme with ample address space. But to nobody's surprise it's taking decades longer than envisioned.
We're slowly transitioning to a new scheme with ample address space. But to nobody's surprise it's taking decades longer than envisioned.