That's because not being allowed to drive is a really harsh punishment. Harshly punishing innocent people is even worse, which is why I assumed you meant guilty-until-proven-innocent.
> it seems like the equivalent of a “but don’t leave town” warning
Not being allowed to drive doesn't keep you from leaving town, but it does severely reduce your ability to participate in society. Now you can't go to work, drop your kids off at day care, or bring home groceries.
> preventing you doing further irresponsible driving is justified prior to the conclusion of the investigation
That's exactly what guilty-until-proven-innocent is!
We can’t expect the status quo to change without some way to force it off the car dependent pedestal it’s perched on. Lawfare might be the best way. If it inconveniences people they might drive different or stop driving so much and then eventually we get urban change.