Here's why:
* Become is an irregular verb. This means it doesn't follow the standard rules of forming past participles by adding "-ed" or "-d".
* Become is already in its past participle form.
Here are some examples:
* He has become a successful writer.
* The world has become a smaller place thanks to technology.
* She became a doctor after years of hard work.
* The house has become a museum.
Remember, the past participle of "become" is always "become", regardless of the tense or the verb it's used with.