The Diamonds seem to be much, much older than other Gems, so that might be part of it. Also, do me one of two favors. First favor: just mess around on your computer and live your life for hour. Second favor: Stand on one leg on your tiptoes, other leg behind you and arms outstretched. Hold that pose for an hour. Do nothing else. Don't speak. Don't move. Hold that pose for an hour. I'll be that second hour will be a whole lot longer to you than the first one.
Pink told Spinel to stand still and wait for her. Even worse, she didn't use her "Diamond command" to do it. She made it a "game." She turned Spinel into the "jailer" for Spinel. All that effort. All that isolation. And for nothing. It's not surprising that Spinel had a murderous psychotic break in the face of that.