Getting convictions is hard, cycling through people is a lot easier. And having to get to work without a car gets the message across,
This is a side effect of our nation being built around the car. In most U.S. cities, let alone in the suburbs, trying to exist without an automobile is at best isolating and will often lead to loss of opportunity. Potential employers judge you in part by your car, and if you don't have one they may well decide that they can't expect you to get to work reliably.
Since you reasonably need a car to participate in our society, driving should be a right and the focus should be on helping people defeat alcoholism. That, however, would require that someone act like they care about that person, and by and large we don't actually give one fuck about one another. We just don't want people inconveniencing us on our way home from work.
Or, and here's a novel idea, we could restore our public transportation systems to the track they were on when the auto companies destroyed them. Then our society could easily absorb the cost of taking driving privileges away from people, since they could still reasonably function in their daily lives, and the debate over whether it's right to terminate people's driving rights would be a much simpler one because it wouldn't interfere with their human rights.
TL;DR: We intentionally rebuilt our society around the car, you can't just take away people's driving privileges because without treating them as rights our society doesn't work.