Could someone explain the grammar behind these more advanced example uses of the の particle?
I've seen many sentences where の is used in ways that I don't particularly understand. For example, these sentences came up when explaining the anime Konosuba (some anime where a person dies and is revived in some parallel world (異世界）lol):

死んだ人は「どうして優しくしないのか女神に聞きました。」 - The dead person asked "Why are you being so mean?"

ニートは「大丈夫です。あなたは女神なのだから格好いい魔法を使うことができます」と言いました - The NEET said "It's alright. Since your a goddess, you can use cool magic."

Question

Could someone explain the grammar behind these more advanced example uses of the の particle?
I've seen many sentences where の is used in ways that I don't particularly understand. For example, these sentences came up when explaining the anime Konosuba (some anime where a person dies and is revived in some parallel world (異世界）lol):

死んだ人は「どうして優しくしないのか女神に聞きました。」 - The dead person asked "Why are you being so mean?"

ニートは「大丈夫です。あなたは女神なのだから格好いい魔法を使うことができます」と言いました - The NEET said "It's alright. Since your a goddess, you can use cool magic."

Answer

I guess なのだから is usually used in the books, dictionary  or anime, we dont really say it in real life なのだから means なんだから。 hope it helps

Answer

なんだから is a broken pronouciation of なのだから.
We say it because it is easier to pronounce.

女神なのだから　＝ 女神な　（＜　女神だ）＋　の　＋　だ　＋　から

This の literally means "thing", or "fact"

”because of the fact that you are 女神”