There are several ways that you can get an ‘‑n’ added to the end of an attributive adjective; hopefully I can remember them all:
- In the accusative masculine (singular), always;
- In the dative plural, always;
- In the genitive masculine or neuter (singular), always;
- In any case of the plural, when preceded by an article (or by a possessive adjective);
- In the dative or genitive of any gender (or number), when preceded by an article (or by a possessive adjective).
(There is some repetition in this list.)
In this case, we have the accusative plural (not accusative masculine, not dative plural, not genitive anything), and there is no preceding article (nor possessive adjective), so no ‘‑n’.
Wikipedia has a big table (actually a set of three, one for each kind of possible preceding article) here: https://en.wikipedia.org/wiki/German_declension#Attributive_adjectives. It looks like I didn't miss anything!