"but Daddy, why did you cut my hair? Mummy liked it long!"
I have a headcanon where the reason Dean always keeps his hair short is because right after his mother’s death, John cut his hair (like the drawing above) because Mary always liked Dean in long hair.
Dean’s hair was also golden, like Mary’s, and John couldn’t stand the reminder of her.
This would also explain Sam’s long hair; he always rebelled, always argued with his dad. So when John told him to cut his hair, because Mary used to like long hair on her kids, Sam would argue back and insist on keeping his hair long, while Dean was always the obedient one.
I just needed a reason to draw sad weechester!dean