Why aren't most suspension bikes extremely long travel? Considering that all mid-range rear shocks have a setting to limit the travel (called oil gate CTD or equivalent?), why wouldn't most frames be designed for extremely long travel?
What is the biggest factor that influences this?

Is is it that a frame with compromising geometry between cross-country and downhill geometry (head tube angle, chain stay length) can't exist?
Is it because of the added weight?
Is it because many people ride cross-country and don't imagine they will ever enjoy rougher sections of the trail?
Maybe the price is the main reason?
Because:


Long travel bikes have a particular geometry which only benefits descends. Applying long travel on an XC geometry bike will create a bike which is not good for anything.
Long travel absorbs a lot of energy. XC riders would not like this.
Long travel requires stronger construction to avoid flex. This means more weight.