One problem is that even taking into account the status quo reset, 2 did a better job of that than 3 has as well.
The first episode of 2 directly addresses stuff fans wondered and debated about in Storm the Castle, from the very first segment: what was that magic Star used to break the cage, is Butterfly magic limited to the wand, is Star's wand broken or what, etc. Even a bit of character development stuff with Star choosing to ask Moon for help after avoiding her for all of 1. Second segment goes heavy into Ludo development, answers more stuff like what could have happened to Toffee and the crystal fragment, and inspired a ton of speculation with the great status quo shift of Ludo now having a wand as well. Even with some dumb episodes like Red Belt and Star vs. Echo Creek following, that was pretty much the best start to the season they could have possibly done, confirming the show would be more plot-oriented and beginning with addressing stuff the audience actually cared about.
The first new S3 episode after the movie is just "oh no, my hoodie that smells like Marco." We don't really learn anything new, Star's crush on Marco is put aside immediately afterward, the reason for their separation is poorly explained, and the Lavabo bullshit feels like it might be setting up a squire/knight plotline, but turns out to be nothing because Marco quits like a bitchboy 3 episodes later. Second segment feels like lore with Glossaryck, but then nothing really came of that either.
The post-movie episodes started out weak and just kept that tone for the rest of the bomb. I almost feel they got lazy this season or something, or maybe more likely that for S2, they had more to prove: many people hadn't given Star Vs. a chance then or just saw it as a mindless comedy with no plot, so they had to start serious out of the gate the second time around, while they have a more established fanbase now. S3 feels like it forgot everything they learned how to do plotwise in S2.