Here is my hot take. Could be wrong. But I think I'm right
The Force Awakens was an experience that everyone wanted to be a part of it was the start of making the prequels right. JJ was on board and nerds like us and normal people were all
The movie got rave reviews. And why wouldn't it. It was A new Hope packaged with some new characters. When the movie ended, there were two groups. Ones who questioned who rey was, what was Luke doing and who was Smoke. Then there were people who left enjoying it but not caring for anything else about it when they left their seat.
Rogue 1 gets sandwiched in between. While many loved it, people like my wife who went with us, didn't hate it but was like Ok.
So by the time this comes out, I think there was a significant amount of people who just didn't care about the continuation of the story. I'm not talking about us. We all saw it. Some saw it twice. But the ones who didn't think about it when they left the theater in 2015, didn't need to rush and see it
Add in the fact of the mixed reviews and you get a major slide in tix sales. Just my take. And I do believe it won't matter. They will milk this cow or Thala Sire for a long time. When star wars land and the accompanying hotel opens in Disneyworld, it will only add to the universe.