Because the "n" in listen is not stressed, that is to say, when pronounced, the stress is on the first syllable. So this "n" does not meet the condition of double writing.

Rules for adding ing after a verb: Generally, add -ing (present continuous tense) directly after the verb; the verb ends with a silent -e, add -ing to -e; stress the closed syllable For verbs that end in -ie, double the final letter and add -ing; for verbs that end in -ie, change it to y and add -ing.

Extended information:

Common double-written ending letters, plus -ing:

1. put-putting

English ?[p?t]; ;Futures trading

he?undressed?the?child?before?putting?her?in?the?tin?bath.?

She took off her clothes and then put her Put it in the tin bathtub.

2. shutdown-shutting?

English?[?t]; American?[?t]?　?

v.?Close; close; stop ; adj.?closed; ceased business; n.?closed

Do?you?mind?shutting?the?door?

Please close the door.