According to this information, why did the song writer Vincent Berry II said that the he couldn't sign the contract because it's a high interest loan? Why is that?
From Wikipedia, who quotes an article of the Los Angeles Times:
Beyoncé received "Sandcastles" in February 2015, more than a year after the song was written. Berry, who was homeless at the time when the song was included on the track listing of Lemonade did not want to sign a publishing agreement and opted out for keeping ownership of the track, saying: "I wanted to own it and that's a harder road. That meant being homeless and sleeping in cars and garages and studios and that's what I was willing to do. I knew I couldn't sign a publishing deal knowing what they are - essentially a high-interest loan. Why would I take that kind of deal?"
Eventually, he received a call from the singer's team notifying him that the song he wrote was included on the album, along with a production credit he would share with Beyoncé.