Ummm. Wouldn't that be because virtually none of the cars have been out there long enough?
Maybe not in the US, but they have been in use in Japan for many years. Toyota has a Hybrid mini van called the Estima that is slightly smaller than the Siena that's sold here, so I'm hoping they'll do a Hybrid Siena here in the US in the next few years. I guess if they think there's a market for it, they will.
I think Prius has had cars out since around 2000, although the new generation was started in 2004.