My guess: time crunch/ trying to fit the whole story into a set amount of chapters. Publishers are harsh
I get it, but it feels dumb. I'm not asking for an adaption that's line-by-line identical to the novel, but I don't understand why they prioritized the School Arc. It's the novel climax, I get it, but it's really badly written even in the novel. They could have gutted that part of the manga and only shown how the people the FL actually interacts with were affected by Alois' plot, and had room to show that the ML and FL are actually in love.
Just because it's an "isekai'd into an otome game" setting doesn't mean that you have to focus on that part of the story at the expense of literally all character interaction.
If you want to understand what's going on, I'd recommend reading the novel. Reading the manga is like trying to read a good book after someone has torn out half the pages. I had hope for like the first chapter, but things went downhill fast.
Seriously, what was the manga-ka thinking to skip half the shipping scenes to focus on THIS mess? It's a romance novel!