It's also pretty trivial for smokers to grow a few marijuana plants if disposable income gets low. There goes that tax revenue. Cigarette tobacco on the other hand requires more processing and growing it for personal consumption generally isn't done.
This fact - that weed is not an industrial crop solely amenable to cultivation by industrial agriculture - is one of two major reasons that weed isn't legal and tobacco is.
The other is that grass makes the citizenry less economically productive.
