I don't understand reddit artists

What's with people on reddit posting highly polished work and calling it a sketch? If it looks like you spent 10+ hours on it, imo it's definitely not a sketch. Or like when people post something with the caption "first time using watercolor" and it looks like it's the 800th time they've used watercolor. Why does underselling your own work and talent seem so common? To me this undercuts the actual sweat and struggle that goes into making a really intricate piece of art. I'm fairly new to reddit but this practice seems really bizarre. Am I alone here?