Steven Universe Theories (Continued)

Where are the other Diamonds?

In, "Message Received" Yellow Diamond asked her Pearl, "Why is there someone on the Diamond Line," as if she wasn't expecting anyone to use it. But if there were more diamonds, shouldn't she have expected a diamond to be calling? Why was she surprised that someone called if the diamonds communicated through the use of the line? That's because the others aren't around. It's just her.