It's partially a social justice issue, as we've managed to build up much of our country in such a way that walking and public transport are geometrically impractical, so poor people would be trapped at home if we banned them from driving the ill-maintained car they're barely able to afford to own and unable to afford to maintain.
It's only done every two years, however.
It is interesting, though, that road safety and risks to other people in traffic are not a big enough thing to trump the social justice angle (right of poor people to drive), but the environment card (emissions) is.
There is a weird logic to all this. Air quality makes a noticeable improvement in everyone's lives and, paradoxically, driving is so phenomenally dangerous and so unavoidable that people don't worry about the very minor factors like the one in twenty who isn't paying attention to their brake pads when assessing that risk.
It might be that the high-pitched squeal built into brake pads to notify people of impending doom is actually doing its job, though.
That is surprising, because it should be fairly obvious that if a car has brake failure, it could be lethal to anyone who happens to be in its path. Same goes with catastrophic failures of the steering system, although those are perhaps even more rare.
Without digging up statistics, I'd say technical failures of vehicles are not a very common primary reason for fatal accidents in West Europe. Bad tyres surely are sometimes a contributing factor.