There is only one thing that causes a corn on the toes and that is too much pressure on an area. When pressure on an area of skin increases, the skin thickens up to protect itself – this is a normal and natural process. If that pressure keeps going, the skin gets so thick that it becomes painful. If that area is diffuse it typically causes a callus and if that area is more focused, then it causes a corn. If you get rid of that excessive pressure, then the corn or callus will go away.
The reason for that area of increased pressure could be multiple different things or a combination of different things. This will need to be dealt with if you really do want to get rid of a corn.
The cause of that higher pressure could be poorer fitting footwear that is too tight and increases pressure on the toes. There could be a bunion that increases the pressure from the shoes on a big toe. There could be a hammer or mallet toe that will also cause increased pressure from the shoe or from the ground on the end of the toe. There could be anomalies in the shape of the bones in the toes that increases pressure between the toes leading to a corn between the toes. There could be any combination of other factors that lead to that increased pressure. You may need to see a good podiatrist if you want to properly identify the reason for a corn and have something done about it permanently.