"key motivation" is a correct and usable phrase in written English.
Example: The key motivation behind the company's decision to expand into international markets was to increase their global presence and boost profits.
He said: "The prospect to work with such a motivated and dedicated group of players is the key motivation for me".
It is also seen as a key motivation behind most tax inversions.
Donohoe cites the societal pressure for constant happiness as a key motivation behind the work.
They wouldn't do that if the key motivation was simply to reduce their tax bill".
The horror of the Holocaust serves as the founding narrative legitimizing European integration, and it's the key motivation for hate-speech laws on the continent.
Certain prizes can bring reporters numerous benefits, including greater freedom in choosing future topics to pursue — in itself a key motivation for some reporters.
Regan cited Scotland's dismal start to their World Cup qualifying campaign – they lie bottom of Group A – as a key motivation in Levein's sacking.
Krzanich noted that a key motivation for his backing of the company's initiatives was that he has two daughters of his own.
Personal development is a key motivation and I am always reflecting on this to make sure I get the most out of each experience.
Making work pay was meant to be a key motivation for the shift to universal credit, a radical redesign of the benefits system spearheaded by Iain Duncan Smith, the work and pensions secretary.
Jews were not the cause of World War II, but they were at the metaphysical center of that conflict nonetheless, since the Holocaust was part of Hitler's agenda and a key motivation of his campaign.
