The origin story of Hypothesis was really that I just wanted to learn Python and needed to come up with a project to hack on in it. For some reason property based testing had been on my mind recently (I'd previously used ScalaCheck a fair bit), I looked around and the available Python options seemed... lackluster (I've since found paycheck which actually predates Hypothesis and is pretty good), so it seemed like an interesting choice of project.
It really shows in early Hypothesis that my progression had gone Scala -> Ruby -> Python.