It is easier to get away with a lie about the value of the drugs. $2000 a pound? Maybe for premo bud. Not for stems and seeds!
When they say "street value", they typically mean "as sold in smaller quantites" as opposed to wholesale values. It appears here, they may have simply determined the value based upon a 1/4 bag selling for $30-$35. $30 x 4 quarter bags = 120/oz. $120 x 16 = $1,920 per lb.
They never use wholesale prices because the ignorant public equates higher dollar values with a more devious person who mus be thrown in prison to protect all of society.