There was an article a while back in the Atlantic Cities that touched on this, as they pointed out, a big part of the problem is that in much of the US there's no practical* alternative to driving. Someone with a suspended/revoked license may have to pick between respecting the sentence imposed on them by the law (and risk further punishment) and be able to work, shop for food, meet family commitments, etc. Revoking/suspensing drivers licenses might serve as a deterrent to dangerous driving (at least for someone who's aware that they're just one infraction away from that), but it shouldn't be surprising that taking someone's license away isn't very effective when used as a penalty.
*- bike commuting is great, but let's be honest, it's not an immediately practical option for someone who lives 30 miles from work, doesn't own a bike, and hasn't ridden a bicycle for decades at the time they lose their drivers license.