Answer: Why not The pen is easy to be written with

When certain adjectives appear, such as easy, hard, difficult, comfortable, etc., they often form sth/ sb be +adj + to do structure. For example, the coat is hard/difficult to wash.

The problem is easy to solve.

The house is comfortable to live in.

Fixed usage, you can use active to represent passive later. In fact, there be sth to do/to be done are all consistent with English grammar. This is the rule of the foreign devils, and there is nothing you can do about it.