Here's why:
* Regular verbs form their past tense and past participle by adding "-ed" or "-d" to the base form (walk - walked, play - played).
* Irregular verbs have unique, unpredictable forms for their past tense and past participle.
In the case of "listen":
* Present tense: listen
* Past tense: listened
* Past participle: listened
As you can see, the past tense and past participle do not follow the regular pattern of adding "-ed" or "-d".