Maybe increasing cannabis production in x4 would help the people invest in them, more people buy and sale fertilizers at a good price, It helps to new players and players focused in farm robbery to grow faster.

It is only an idea.

There's currently an update in the works which would increase the worth of cannabis already, and the reason people don't invest in cannabis production is that selling fertilizer makes more money that selling the cannabis since the cannabis is barely used for anything.
At the very least wait to see if there isn't more people investing in cannabis once smuggling is out.

Increasing the production of it would decrease the value though... Supply & Demand, if you want the value of something to increase you have to make said 'thing' more difficult to obtain :)

The drug is not useful, definitely not in the quantities supplied. So it's pretty much driven by Drug Den sale prices, or should be, but fert prices have been disproportionately high for as long as I can remember.

I can only put it down to players not knowing they are losing money and buying the fert regardless, or possibly some very long term speculation on Cannabis price.