World of Warcraft implements undocumented item level scaling in patch 7.2
The reward scaling in World of Warcraft has always been pretty straightforward. At the start of the expansion, everything at max level is a pretty close match for you; by the end of the expansion, all of that work you put into acquiring better items pays off because every enemy lies dead at your feet. It’s how things work. Sure, there are a larger number of things at your level in Legion due to scaling, but the way gear works remains constant. After all, if you made enemies scale with gear, you’d have no reason to actually get better gear, so you would… oh, wait, they actually did that with patch 7.2. Huh.
Yes, this is something players noticed, and according to Ion Hazzikostas on the forums it is completely intentional. The developer rationale is that it allows for creatures to scale more organically to various gear levels so that open-world enemies never became trivial or easy for players. The intent is for enemies to scale up slower than gear level (so gear still feels like a reward) but still scale with your power in terms of items.
So, get excited about the next set of world events! They promise to reward you with gear that makes everything else around you stronger as well, making the effort put into acquiring that gear a complete waste of time.