Pretty much every day Amazon advertises a film to me that I watched on the same platform's account a couple of weeks ago. Presumably it also knows enough to determine that the account isn't shared so it's not advertising to other family members or something.

For all the billions spent on ad targeting, it's pretty coarse.

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.