Why didn't they accept my work?

To be honest, I don't see much commercial value in this. I'm not sure customers would pay for it.

Eighth notes are not unique. They're easily created from custom shapes in Photoshop. See screenshot.

This looks very close to the iTunes logo in my opinion, and I think it would be rejected on IP grounds if it passes the standard for quality.

Giving us the reason Adobe listed for the rejection helps us give you a more accurate answer and also saves us time from having to guess.

Cheers!

It doesn't look very sharp, and it's underexposed. I suppose the refusal was on quality issues.