I wish I could say I'm surprised, but I'm not.

We re-homed a cocker spaniel, Dusty once. Our friend had found him on the freeway, and we had decided to adopt him. However, he HATED little kids, and my siblings were both very small. He was a nippy dog, and nippy + hating little kids just didn't work for us. We found a retired couple whose grandkids lived several states away and who had experience with nippy dogs. Last I heard he was doing very well, and had just had surgery to remove a cataract from his eye.

We also re-homed another dog when I was very small. I don't feel that the reasons were adequate, but I was only seven.