That was probably because it would have been interpreted as cutting and running, given Foreign Affairs Minister Murray McCully had announced as recently as May that the PRT would not be pulled out until the latter part of next year.
The subsequent three deaths at the weekend have changed everything, however. Key desperately needed a bone to appease those who want the troops out forthwith.
It appears April next year is now the favoured date as that suits one of the international coalition partners willing to help the New Zealanders with the logistical demands of "transitioning" out of Afghanistan.
Key did not say which partner. But April will not come a moment too soon for him. The weekend deaths may well awaken what could prove to have been a sleeper issue in domestic political terms - and in a fashion which is hardly likely to benefit the major ruling party.
Up till now, New Zealand's decade-long military presence in Afghanistan has been of little consequence for most people.
That indifference has been reinforced by public acceptance that one of the roles of the Defence Force is to play a constructive role in keeping the peace that others have made - thereby enabling New Zealand to be seen to be pulling its weight internationally.
The public has become hardened to things going wrong on long-term deployments such as to the former Yugoslavia or Timor Leste. Judging from on-line comments from readers, death is simply seen as part of the soldier's job description.
Above all, National and Labour have by and large reached a consensus on the necessity of most deployments.
For an issue to cause governments strife, public opinion has to be strong, the weight of that opinion has to come down heavily on the other side of the argument to the Government's position, and the major parties need to hold sharply contrasting stances.
Afghanistan has so far failed to pass those tests. With Labour, however, calling for the troops to be brought home "as soon as practicable", the politics may just be beginning.
Five deaths within two weeks may yet turn out to be a statistical blip. But Key cannot bet on that. With the insurgents and the Taleban targeting the PRT, delaying full departure until September next year could have yet more gruesome consequences, not only militarily, but politically as well.