I think tobacco HAS been used in the same way, actually.
And I don't think that anyone was asking about Why there wasn't "tons" of them being made and shipped. The answer that comes to my mind is that they were probably never mass-produced for the illegal drug trade. Maybe for all the reasons you said...."too dangerous"...."too much work"....are the reasons why only a few people, who were connected to the Vietnam War in one way or another, got in on them. The reason why more people don't know about them or were exposed to them, is because they were a limited-time-only kind of thing that were made available when they were sneaked over on military cargo planes during that war.
After the war ended and all the vets and Peace Corps workers had returned, opiated Thai sticks pretty much disappeared. I never got any of them ever again. I never even heard about any of them being available, again. There wasn't like an ongoing demand for them or anything because most of the people I knew didn't like the idea of using opium. That was going just a bit too far for the weed-smoking crowd that I hung with.
I reckon it was just a passing thing that happened during that time and then faded out like bell-bottom pants. Nevertheless....very real.