It USED to be a cute romcom about a straight laced student and a misunderstood teacher, but now it's...
Checks notes
"The Author's challenge to the Editorial Department to see how many unlikable side characters they can cram in before getting axed."
Edit: Joking aside, knowing what I know about the manga industry, my guess is that it's actually the other way around and, because it's a romcom, the editor(s) said, "You can't just have these two, you need side characters to help move the relationship forward," or something stupid like that. Honestly, that would be funnier, since the relationship moves forward with the most ease when it is just the two main characters with no side character influence.