That's a very good question.
Of course 100 years ago, when there was no treatment available at all, a third of people would spontaneously cure, another third of people would get sick and die, and the last third would go on to develop chronic TB symptoms. They would be transmitting the TB germ to others.
In this day and age we have a new wrinkle, and that's called HIV. People with HIV almost invariably, if they develop active TB, will go on a downward course and eventually die. The thing is that before they die, they tend to transmit that TB germ to...well, it depends on the community, but often to dozens of other people.