There are several reasons. Maybe they miss you and want to know what you're up to. Or it might be that they're comparing their lives to yours. Sometimes, it's just a habit or they accidentally came across it.
Sometimes exes watch your story because they want to see if you're doing well or if there's any chance of reconnecting. Maybe they're just bored and going through social media feeds without much thought.
Maybe they still have some interest or curiosity about your life.
Some exes watch your stories because they haven't fully moved on and still have lingering feelings. Or it might be a subconscious habit without any deep meaning behind it.
It could be that they want to keep tabs on you for various reasons. Maybe they miss you or are just nosy. Sometimes it's just a random act without much meaning behind it.
It could be that they relate to the characters or the plot. Sometimes, it's just for entertainment or to pass the time.
Maybe they're just curious or bored and want to see what's up.
I watch my story mainly because it makes me feel good. It can be inspiring, funny or touching, depending on the moment. Also, it helps me relax and forget about any stress I have.
Maybe they find it interesting or engaging.
Maybe they're still curious about your life but don't want to engage directly. It's a weird and confusing behavior.
Maybe they do it to keep tabs on you or to satisfy their own sense of control and superiority.