basically you'd like to change around the entire market.
either everyone that grew, would have to sell at bare minimum so the dealers could sell for whatever, or the dealers would all have to grow.
as has been said, it's a business, and i'm pretty sure that just partly, it's to do with organisation, knowing what is going where etc etc etc.
if i bought a pound, and started selling it off in utterly random quantities, i might get halfway through the thing and realize i've made 1/4 of my money back, so the next half is outrageously priced, or you might get home, open your stash to bag something up and think who the fucks been pinching my bud due to not having any idea how much and such has gone. it's a little thing called convenience, organisation etc.
but sure, in an ideal world the dealers would be picking up for penies as they should (like how can a grower not comercially shift for £100 an ounce, why the hell do they think they can sell to the dealers at £160, that's stupid and greedy!) and then the dealer can sell it on in whatever manner is best for the market, customers etc etc, and get a good name for his good deals. alas, as these days are, the dealer would then think HAAAAA I CAN MAKE PLENTY PROFIT NOW I'M BUYING SO CHEAP
one thing i can say for the growers that sell wholesale. they sell their dealer an ounce their dealer get's an ounce. you buy same ounce off your dealer and it's suddenly a couple of grams down, or you buy an either and well the weight is just a guggle and you know you'll get anything