Maybe it's because the comic is too exciting and keeps your mind active.
It could be that the light from reading the comic is affecting your sleepiness. Or, the story in the comic has you thinking a lot and making it hard to relax and fall asleep.
It could be that the manga has such an intense plot or interesting characters that it keeps your minds active and makes it hard to relax and sleep. Or maybe the lighting or position while reading is uncomfortable.
Well, one reason could be that the bright colors and fast-paced action in cartoons stimulate your brain and prevent it from winding down. Also, if you get too engrossed in the story, you might keep thinking about it even when you should be sleeping.
Maybe the story is too engaging and keeps your mind active, preventing sleep.
There could be several reasons. Sometimes the lighting is not right, making it hard to relax. Or maybe you have a lot on your mind and the comic isn't helping you unwind. Also, if the comic has a complex plot, it can keep your brain engaged and prevent sleep.
It could be that the visuals or the sounds in the motion comics are stimulating your senses and making it hard for your brain to wind down. Maybe they brought up thoughts or emotions that are keeping you awake.
It could be because not sleeping makes you stressed and irritable, and that stress might come out in the form of creating or relating to rage comics.
It might be that the comic's story is so engaging that it keeps you thinking and prevents your mind from calming down. Also, if you read right before bed, the body's internal clock might not be ready for sleep yet.