One possible reason could be to annoy Harry. Draco is often portrayed as a bully in the Harry Potter series, and stealing Harry's glasses is a way to make his life difficult. It could also be a power play, showing that Draco can take something important from Harry.
In some fanfiction interpretations, Draco could steal Harry's glasses to get his attention. Maybe Draco has some unspoken feelings for Harry that he doesn't know how to express in a normal way. By stealing his glasses, he forces Harry to interact with him, whether it's to demand them back or to figure out why Draco did it. It could also be related to a plot where Draco has been influenced by some dark magic or a spell that makes him act out in this way against Harry.
Well, it could be that Draco steals Harry's glasses as a prank. Maybe he wants to embarrass Harry in front of their classmates. He might hide the glasses in a secret place in Hogwarts, like in an old unused classroom, and Harry has to search for them while dealing with his blurry vision.
One possible motive could be that Draco wants to annoy Harry. Stealing his glasses is a petty way to get under his skin. It's a simple act of mischief that Draco might think is funny. Another reason could be that Draco is jealous of Harry. By taking something so important as his glasses, he feels like he has some power over Harry.
Well, Harry could also be more level - headed. He might try to figure out Draco's motive first. Since he's used to Draco's antics, he could choose to outwit Draco instead of getting into a physical or shouting match. He could use magic in a clever way to get his glasses back without causing too much of a scene.
Maybe it's a form of power play. By taking Harry's glasses, Draco is asserting his dominance. In the wizarding world, status and power are important, and this could be Draco's way of showing that he can take what he wants from Harry, who is often seen as his rival.
Harry could be really angry. He might immediately try to get his glasses back, using some basic spells or just by physically trying to grab them from Draco. He'd be frustrated that Draco is always causing trouble for him.
Well, perhaps Draco initially takes the glasses with the intention of causing trouble for Harry. But as he has the glasses in his possession, he starts to feel a bit guilty or realizes that it's a rather childish prank. He then might return the glasses in a somewhat begrudging yet also slightly friendly way, which could be the start of an unexpected friendship or at least a less hostile relationship between them.
Maybe Draco is jealous of Harry's popularity and power. Turning him into a vampire could be a way to strip him of his status among the wizarding community. Vampires are often feared and shunned, so Draco might think this would be a good way to get back at Harry.
I don't think it's common at all. Fanfiction usually delves into the deeper emotional and plot - related aspects of the original story. Themes like friendship, love, and the fight against evil are much more prevalent. Stealing underwear is such a specific and rather unorthodox concept that it's likely to be a very niche and not commonly found type of fanfiction within the Harry Potter fandom.
One possible plotline could be that Draco steals Harry's underwear as a prank. He might do it to embarrass Harry in front of their classmates at Hogwarts. Another could be that Draco steals it because he has some strange fascination with Harry and it's a way for him to have something of Harry's. Or perhaps it's part of a dare within the Slytherin group that Draco is a part of.
In the 'Draco steals Jarrys underwear fanfiction', it could be that Draco is being controlled by a spell or some dark magic. He has no choice but to steal Jarrys' underwear, and this sets off a chain of events in the wizarding world. Jarrys then has to figure out how to get his underwear back and break the spell on Draco.