Why doesn't my music work without wifi?

I recently bought an iPod touch fifth-generation. Before I got the new one, I backed up all my music onto iTunes. when I purchased the fifth GEN one I restored the music by plugging in my iPod to my laptop and going through iTunes. later that day I noticed that my music would not work and I'm guessing it's because I was not around Wi-Fi.

So my question is, since I restored my music and it seems to be on my iPod why can't I listen to it without Wi-Fi?