They already explained their point.
They wanted to remove the IoW and to rewrite several lores because the original lores were pretty much all written without much thoughts about the future.
When the shurima patch went out they also wanted to take this as a possibility to change the lore format somewhat,giving us short lores in the client and long lores on the official site,but there were technical problems with that,so the shurima(except for xerath and azir who got long lores posted on the forums) champs remained with a short lore for quite some time(same goes for the new champs,though they started to add more lore related content for later champs,like the comic for ekko or the tale for
)
They solved the tech-issues this year and pretty much used the bilgewater event as a way to return the lore,giving us detailed backstorys for
on the main page,while still giving us the short lore in the client(as well as the event-lore).
However with the release of the bilgewater lores they also changed the lore format again.
Originally the lores just described the champ,but over time the lores became more story-like and episodic.However the new full lores consist of a bio(basically an extension of the short lore) and a story about the champ(basically the episodic kind of story that was seen in the previous lores).
However this change meant that the shurima stories that they originally prepared needed some adjustments,as these stories were written in the old format and now that the harrowing was on its way,they decided to focus on the shadow isles champs first and thus gave
their full lores.
So currently only the champs that i mentioned above and
have a lore that is really up to date,the others are going to get completely new lores or at least updated ones(I guess some of the more episodic ones can remain as the "small-story-about-the-champ"-part of the lore).
Since the shurima champs are loreless for so much time now,they are going to be the next ones to get full lores,after that they have set their eyes on mt.targon.