previously downloaded songs keep showing icloud icon
I just upgrade to an iPhone 6 from an iPhone 4, I went through and downloaded all my songs back onto my new phone. I am now noticing that songs that were previously downloaded are showing the iCloud icon. Why are these songs not staying on my phone? I have plenty of space remaining, but certain songs keep showing icloud icon and have to be re-downloaded.
iPhone 6, iOS 8.3