Because they're dealing with an event film.
You're talking about a pattern that is very outdated, where blockbusters and series at their current form are much different to how movies were handled in the 70s, 80s, and 90s. I've even seen people mention 00 movies as being different from the current flock.
People of today aren't going to act different just because it's an older series.
You're just making these rules up just to defend this movie, just like people saying it could be series fatigue.
And even still, Jedi was the #1 domestic release of the year. We're talking about the franchise slowing down when it was the top grossing film of the year. These films operate at a different level than a Guardians of the Galaxy or a Deadpool. Where those caught an audience and had room to expand for the next entry, Force Awakens was already at the top. It's the highest grossing (domestic) film of all time. That's the ceiling right now.
#1 movie on a slow year, where the GotG sequel made more money than the first one and Logan did more money than the first two Wolverine movies.
These movies did well because good word of mouth.
What will happen with Star Wars if it starts getting bad word of mouth? It already started with Awakens and grew significantly from way more criticism with Last Jedi. They're already doing damage control with Solo.
So how will the "Star Wars Event" be like in the future if it's becoming known for being trash? You talk about that built in fanbase, but that fanbase is souring up, where even the hardcore aren't able to stomach it anymore.
Will it be like Marvel comics, where only the casuals defend everything that's going on, making it seem like they're doing great because of their prevalence on social media, while the hardcore are dropping it leading to sales significantly dipping, angering comic shops, and Marvel trying to hide that dip by inflating prices?
The toy sales are up. The movie ticket sales are flat to a bit down from TFA which was the first Star Wars movie in forever so ofcourse it was huge.
Toy sales are up (read: what toy manufacturers sold to retail), but you have to remember that these stores are ordering merchandise that may or may not sell based on the staying power of the movie. The Force Awakens toys harmed sales for Rogue One because TFA toys were shelfwarming on the shelves by a huge swath. So stores couldn't order as much as they could because there was already a lot Star Wars toys from the previous year on the pegs. TFA toys were all put on clearance months before Rogue One toys came out, yet there were dozens and dozens of the same figures and vehicles sitting when Star Wars Day hit.
TFA sales were so bad for retailers, that these same clearanced toys are still on the shelves today in toy stores, but not in as huge numbers as they were last year, hence TLJ getting such a huge push in sales.
So how are TLJ sales in retailer stores doing? Anecdotally, all the toys are easy to find in my area and that isn't a good thing. Popular toys sell out, regardless of how many are ordered.
So there you go, it doesn't matter how much things sell today. What matters most is staying power. TLJ opened big, so big that bad word of mouth really didn't affect its ability to cross over a billion dollars in movie tickets. But that word of mouth did have an effect on its staying power.
Staying power ensures toy sales, as they should be selling well throughout the year at retail, not manufacturer orders.
Staying power, or whatever the correct term for this, is what drives all future sales. TFA did not have staying power, which affected toy sales and maybe movie sales. We'll see what TLJ staying power is like.