Poisson distribution, higher probability of short periods between failures than long ones.
If it is a Possion distribution then you'd expect them to bunch up and get years with none, then them concentrated over a few years.
Possion distributions usually imply a time factor. That's concerning in this case as it implies maintenance isn't effective.
Imagine you throw a three darts a board. Which is more likely: all darts are equidistant, or 2 of the darts are closer to each other than the 3rd? Now imagine it's 3 events in time rather than 3 darts on a board. And the same logic applies to an arbitrary number of events, of course.