That's Why ので

から states a reason as a fact, sometimes bluntly, while ので frames it as a shared, reasonable explanation, which is why it shows up so often right before a polite request like てもいいでしょうか. の-adjectives and nouns take な before ので, just as they do before の itself: 好きなので, 今日なので.

Trailing off after ので, leaving ちょっと。。。 unfinished, is a very natural way to decline an invitation without spelling out a flat no, letting the reason imply the refusal on its own.