With 12 strings jangling all kinds of different harmonics simultaneously, you need a little damping. Wood will do that.
Good of this or that kind, or carbon fiber, or steel or brass bodies, all affect the rate of decay of the notes. On a 12 string carbon fibre just lets the notes hang around too long. Too much information in the air. Confusing. You might say the Rainsong does too good a job. If I had one, I'd punch holes in it.