Really to reiterate what has already been said:
//1. Why wasn't he already in jail ?//
Presumably because any offences he had previously committed were solely excess alcohol (or other summary) offences. The maximum such offences attract is six month’s custody. Knocking off a third for a guilty plea reduces that to four months. He would serve one month of that in custody, one month on “Home Detention Curfew” and the remaining two months “on licence in the community.” If his last offence was in 2018, even if he had been sentenced to the maximum possible, he would have been released long ago.
//2. Why did they wait until he killed somebody ?//
Because, I’m pleased to say, we don’t punish people in this country for something they might do.
//3. Why has he only got 10 years ?//
Presumably because the maximum sentence for causing death by dangerous driving is 14 years. Again, knocking off a third for a guilty plea reduces that to nine years and four months. So he was over sentenced .
//4. Why isn't the driving ban for life ?//
As Andy has said, the sentencing guidelines near enough preclude it. In any case, somebody who is prepared to drive whilst three or four times over the alcohol limit is unlikely to heed a ban if it suits them to drive. The only sanction a court has for either offence (excess alcohol and driving whilst disqualified) is six months’ custody, so see point one.
None of this is the fault of the judiciary. Magistrates and judges can only sentence in accordance with the law and the sentencing guidelines. If you want matters like this addressed you need to lobby your MP. Since (today at least) the Prime Minister seems more preoccupied in preventing half a dozen football teams from participating in a new competition (which I would suggest is no business of government in any event) good luck with that.