The old man might see something in Byleth that reminds him of himself or someone from his past. This connection makes him choose Byleth to be the one to hear his story. It could be a similarity in their personalities, like their determination or kindness. Or perhaps Byleth has a particular skill or talent that the old man admires, and he wants to share his story as a form of compliment or as a way to encourage Byleth further.
Maybe Byleth has a reputation for being a good listener.
Perhaps it's a story related to the history of the place. Maybe he witnessed some important events in the past that shaped the current situation of the town or community, and he wants Byleth to know about it so that the knowledge can be passed on. For example, if there was a great war or a significant discovery in the area, his story might be about that.
Maybe it's a sign of his mental stress or some kind of hallucination. Could be related to a past trauma or a current overwhelming situation.
Maybe the volume of the cartoon is too low or the old man has hearing problems.
Maybe the old man has some health problems in the cartoon's story. That could explain it.
It could be that his mind was preoccupied with something more important, causing him to forget about the socks. Or perhaps he has a memory issue that makes him forget such small details.
Maybe it's part of a magical or fantastical element in the cartoon's story. Sometimes strange features like that add an element of mystery or fantasy to the plot.
The reason could be to give the old man a distinct look or personality. Maybe it's a way for the artist to make him stand out. Or, it could be part of a story where showing his teeth is significant for the plot development.
Maybe it's part of a symbolic act or a plot device to drive the story forward. It could have deep meaning related to the character's development.
He might read it for entertainment. Love stories often have interesting plots and characters that can keep a person engaged, regardless of their age.
Kids that age are naturally curious and asking 'why' is their way of trying to understand the world around them.