Ultimately there are two kinds of people that play, watch and read about this game:
The people who only understands the game itself, which can be given by for example the streamer Yassuo's reaction the the Awaken cinematic
And then there are the players who invest in the story that exists beyond the game, like the YouTubers Necrit and TBSkyen
These three people that were taken as examples are some of the most prominent figures in their respective area of expertise, who all reacted to the same cinematic. One is a high-ladder player who specializes in the game itself and nothing else, while the other two are explorers of the story and lore of what is behind the game. The short answer to your question is that Riot probably tries to invest most of their resources on events that can increase their revenue, such as skin events and E-sports. Meanwhile, the story of Runeterra does indeed advance, but not at the pace one would expect because of the reduced funding for it compared to the other events. While all of us here wish that there was actually some meaningful progress in the game, they cannot do so without the right reasons to do so. So this is as far as it goes when it comes to the pace of advancing the stories.
If you want more insight on potentially why this season could not advance the League lore, TBSkyen has a very interesting view on this while discussing about Sylas. In essence, he discusses about how Riot is afraid to break the "status quo", which refers to the existing state of something, in this case being the story of Runeterra. However, Riot did make a valiant attempt at it in 2015, when they introduced Gangplank's "death" and Miss Fortune's overtaking of Bilgewater, which is still canon. There are also other small successful attempts like the redemption story of Riven and Yasuo.
While I am not a spokesperson for Riot in this regard, I hope it answered your question. We can only hope that there will be any meaningful advancement of the major stories of Runeterra in the future.
