People are also very attracted to brands and swayed by marketing.
I don't doubt for an instant that the marijuana industry is going to be gigantic if it ever becomes fully legal in the US.
A single tobacco plant won't yield much more than 2 ounces and that would last a pack-a-day smoker less than a week, saving them about $40 (not including labor of actually making the class A cigarettes). 2 ounces for a single cannabis plant is a relatively poor yield but would still last an 8th-a-day smoker 2 weeks and save them at least $400 and there is up to a 10x difference between a poor yield and an excellent yield. The reward/effort ratio for these two plants is worlds apart so I don't think the comparison to tobacco is particularly helpful.
I also enjoy trying a wide variety strains, which wouldn't work out so well if I was cultivating only a few plants.