my theory on this is how dry the weed is. when I buy weed at a dispensary, it not only has (usually)been properly dried, it has been sitting on the shelf for long enough to dry further. the resin comes off much easier. when I grow my own smoke, I'm too impatient to wait for all of it to fully dry, in fact I actually rate the greasy, oily smoke that you get when the weed is just a tad "too wet". the resin doesn't come off of the wet weed as easily, and my kief collector stays empty until jan or feb when my weed is finally cured properly.