Why is the 991 Turbo depreciation so fast?

I am in the market for a Turbo or a GT3. I see 997.1 turbos for 70-80k with under 30k miles, yet the 991 turbos are going for 100k with less than 20k miles. Is this just due to the lack of manual and larger production volumes of the 991? via /r/cars http://ift.tt/2uKWs9n