Really in the case of tobacco, (almost) no one is going to grow it. It's a massive pain in the ass when most people are addicted to the nicotine. Synthetic nicotine in vapes are what would be black marketed these days.

It's way easier to ship as well discreetly, borderline impossible to seize in reality, which is probably one of the reason in SEA they are about to ban vaping, it's really a huge gateway to transport anything, very rarely LE is opening open and testing what the vape contains, so transporting large amount of any substances has never been easier.

Weed and tobacco smoking are also easy to detect by people who don't want secondhand smoke. And if it were illegal, they could report it.