They're probably not forgotten but it is still a bit silly after 3 years only we heard a new support item that is called as Eye of the Watchers and some informations from Bard's teaser. They have extremely high potential, they can change story in good way. Everybody waits for Ao Shin, as I do but it's really sad no one is remembering them.
Simply because lore has become rather scarce. Don't get me wrong,the new lore is awesome,but there is still A LOT of lore that needs to be reworked(or at least updated) and something as major as the return of the watchers would probably need some kind of event on its own.
They probably want to focus on the problem zones first before they start to expand on the old ones(you might argue now that they expanded upon bilgewater twice now,but the second part was a good opportunity to focus on the shadow isles and tease the new champ as well) I am pretty sure that they already planned the general direction for the new lore back during the freljord event,so I think it is pretty safe to say that this is going to stay. Maybe some individual lores are going to change slightly,but thats about it
The original, and somewhat debunked, theory is that they were creatures from the Void. They were not physically thrown down the cliffs of the Howling Abyss, but rather banished back into the Void itself. This theory also states that behind the gate on the purple side of the Howling Abyss map is a closed portal to the Void.
I don't remember most of the details supporting the theory, but the artwork surrounding the Watchers and that side of the ARAM map was a big part of it. That was, of course, back when the old lore was already fading. It's possible Riot had already begun planning the new lore at that time, so it's possible we won't have any reliable sources until the next Freljord story that specifically covers Lissandra and either her history or her future plans comes out.
