んですもの

because; after all

→ の
phrase Rare #22,515
because; after all An emphatic explanatory ending used to give a reason or justification, often with a nuance like “you see” or “after all.” It is especially associated with feminine, gentle, or somewhat old-fashioned speech.
JA: だって、今日は特別な日なんですもの。
EN: Because today is a special day, after all.

何も知らないんですもの

I don't know anything, after all.

— レベッカ (1940)

だっておかしいんですもの

But it's strange, you know.

— 生きる (1952)

皆がじろじろ見るんですもの

It’s because everyone keeps staring at me.

— レベッカ (1940)

あたし勘違いしてたんですもの

It's because I misunderstood.

— 生きる (1952)

もちろん私はまだ若い政治大人やっているんですもの

Of course—I’m still young, and politics is something adults handle.

でもわたしたち全然共通点がないんですもの

But, you see, we don't have anything in common at all.

二人とも自由好きなんですもの

They both like freedom, after all.

— シティ・オブ・ゴッド (2002)

責任者責任を取る為にいるんですもの

The person in charge is there to take responsibility, after all.