Why writing on a glass with a pencil is difficult?

Whenever you are writing with a pencil on paper, there exists friction between the pencil and the paper. The pencil's tip is made up of graphite. The particles of the graphite get deposited on the irregular surface of the paper. It is because of the friction; the graphite is reduced into bits and gets deposited on the paper. Hence, friction plays a significant role in writing with a pencil.
As the glass is finely polished, it has very less friction and does not give enough friction for the graphite to get reduced into bits and deposit on the glass. Therefore, it is very difficult to write with a pencil on a glass.