That's because most of them were. Stone was the easiest to make them out of and didn't cost as much as getting metals together.

[Sweet continues to dance, but then begins to tip-toe its way up his arm. If he lets it, it will settle on his shoulder, pressed up close to him.]

Sweet Pea here has only been purposed to recognize tone and gain a sense of your mood from how you talk. Probably why its showing off for you. To get a stronger emotional reaction. It's supposed to be a cuddle buddy.