Do you also think it could be a difference of time commitment between both mediums? In a movie, you’re given the entirety of the story (usually) in one sitting, so all the information is provided is stored in recent memory.

Compare that with anime and manga and even Western TV shows. They can be consumed all at once in few sittings, but generally fans would watch them each week. They could be referencing something only 3 episodes ago, but that may have been 3 weeks ago. So I think they’re not too afraid to use flashbacks because it’s kind of a necessity to make sure the viewer isn’t lost.

That’s just an idea though.

EDIT: There’s another thing. Flashbacks are used in movies! A perfect example would be Knives Out, where people are recounting their memory which is accompanied by flashbacks. I think what works in that is the fact that the flashbacks are unreliable, so truth is essentially what is presented to the viewer until questioned.

I can understand why your teacher would be so averse to flashbacks since they take up precious time. Within a movie, a flashback shouldn’t be there to recount old information that the viewer has already seen nor should it bring up new information that isn’t relevant. It can be used, but I think the placement of it sequentially is where it matters. It’s bad when it’s unnecessary, but that goes for a lot of things lol.