Well yes, Key even explicitly mentioned this factor in his resignation speech:
It gives the Cabinet and caucus plenty of time to settle in with a
new leader before heading into the next election with a proud record
of strong economic management, a commitment to the most vulnerable in
our society and lots of ideas to keep lifting New Zealanders up in the
It would be easy to say I have made this decision solely to rediscover
the personal and family life I once had, and that is a factor, but it
is one among many.
Over the years I have observed many leaders who, in a similar
position, fail to take this step.
I can understand why. It is a hard job to leave.
But, for me and the National Party, this is a good time to go. Party
membership is high and the party is well-funded. The caucus is
talented and eager to serve, and one of the achievements of which I am
proud is having built with my colleagues a Cabinet team that is
capable, committed and cohesive.
Ardern wasn't as explicit, but she did mention it in passing:
My opportunity to thank the many people I need to will likely come in
April when I depart Parliament, 15 years after having been sworn in.
Till then, I see my role to help the Labour Party, who I consider to
be my family, navigate this next phase; and then, to leave the next
colleague who takes on this role, all the space they need to make
As for what the leaders' 'real motive' is - I think it's fair to say that their relative decisions will have come as a combination of reasons. If a leader is intending to leave the leadership position anyway; as both Key and Ardern suggested, it seems disingenuous to lead their party through an election campaign when their heart isn't in it and they have no intention to stay in the role to deliver on any of the promises they are making. The best course of action, not just for their party, but for their country - I would have thought - would be to allow a new leader time to establish themselves before facing the country at the ballot box.
So yes, it's definitely a consideration that factored into the timing of the resignation announcements of both leaders, but I don't think it's necessarily a bad thing for them to want to ensure that the party they have supported during their political careers has a stable transition of power and the best possible opportunity to establish a coherent new leadership before the next election.