"Contentment is a creativity killer, but don't worry - I'm very capable of making myself discontented."--Florence Welch

This quote presupposes that we can be content, and we can--but not for long.
We're human.  We like variety, no, we need variety and, as the old saw goes, necessity is the mother of invention.
We can get bored with contentment and so we look to spicing up our daily bread with a pinch of creativity.
In short, I don't agree that contentment is a "creativity killer".  Contentment can lead to boredom,  but boredom is a rich soil in which creativity thrives.