It's not to get you to watch that specific movie again, rather its purpose is to remind you that you watched something you (hopefully) enjoyed on their platform so you are more likely to keep doing so.

If interrupting a video to remind me that I watched a film (that I didn't even especially like) two weeks ago is the best modern big-data AI-leveraging advertising tech can do maybe adtech isn't worth all the data centres full of GPUs crunching the data.