It could be for comedic effect to lighten the mood and add some fun to the story.
Maybe it's a name from Merlin's homeland or has some special meaning in the lore of the fanfiction world.
If Merlin died in the fanfiction, it could trigger a series of tragic events. The balance of power could tip, and the villains might seize the opportunity to attack. It could also bring out hidden strengths in the remaining characters as they try to cope with the loss.
One reason could be that other characters are more popular. For example, if there are more 'flashy' or relatable characters in the source material, they might draw more attention in gen fanfiction.
Well, in many fanfictions, Arthur might be overprotective of Merlin because of their deep friendship. They've been through a lot together, facing numerous dangers and challenges. Arthur has come to rely on Merlin in many ways, and he doesn't want to lose him. So, he becomes overprotective to ensure Merlin's safety.
Merlin is a very interesting character. His magical powers and his role as a servant with a big secret in the original story make him a prime target for fanfiction. People like to write about him because they can explore his untapped potential in their stories.
In fanfiction, Arthur might be rough with Merlin because of a prophecy or a pre - ordained fate. He might think that by being tough on Merlin, he can prevent some bad outcome that he believes is related to Merlin. For example, if there's a prophecy that Merlin will bring great change to Camelot, Arthur might be rough in an attempt to keep things as they are, out of fear of the unknown.
In a more humorous take on the 'Merlin tied to a bed' fanfiction, it could be that Merlin has fallen ill and the overly - protective Gaius has tied him to the bed to make sure he rests. Merlin, being the active person he is, complains constantly. Arthur comes to visit and teases Merlin about finally being still for once. Meanwhile, Merlin tries to convince Arthur to let him loose, promising that he'll be fine. Eventually, Gaius relents and unties Merlin, who then immediately starts bustling around the room.
One more idea is that Merlin is tied to the bed in a dream - like state created by an ancient magic. In this dream world, he is faced with his deepest fears and insecurities. His friends in the real world notice his strange behavior and try to wake him up. Merlin, while in the dream, has to find the source of the magic that is binding him and break free. Through his inner strength and the memories of his friends, he manages to do so and wakes up, having learned more about himself and his magic.
If Merlin is a Dark Lord in fanfiction, it could be an interesting exploration of the 'nature vs. nurture' concept. Maybe he turned dark because of the constant fear of being discovered and persecuted for his magic. His actions as a Dark Lord might include taking over Camelot or exacting revenge on those who wronged him in the past. It gives a whole new perspective on his character.
Well, Merlin is a fictional character and doesn't have a physical form to actually 'eat' anything, let alone fanfiction. Fanfiction is a written work created by fans, and it's not something that can be consumed in a literal sense by a fictional being like Merlin.