In a real nutshell, as our Sol system travels around the Milky Way
galaxy (circling its center once every 250 million years), we encounter
celestial bodies and other matter that may do things like disrupt comets
in the Oort Cloud and Kuiper Belt and send them moving towards the Sun,
where some might end up hitting Earth - like one apparently did 65 million
years ago, creating an adverse affect on the dinosaur population.

The authors of this paper state they have found a correlation between
our movement through the galaxy and extinctions on Earth, roughly
corresponding to every 62 million years.

So we may be overdue.