It should be obvious why Earth experiences mass extinctions. The Solar System takes about 400 million years to complete an orbit around the galactic center.
The Solar System is not standing still. At points during that orbit the Earth and the Solar System encounter meteors.
it's 225 million mile ride at 250km/s that gives us roughly 8 points of extinction if the cycle is every 27million years.
Our galaxy has 4 major spiral arms and several minor arms with 'space' in between the arms. During our 225 million mile ride, we transverse these arms. Our Sun is currently transiting the minor Orion spiral arm. It takes about 10 million years to transit the arm. (That's also the lifetime of a ‘massive star’ formed and remaining within the arms, which eventually becomes a black hole or a supernova). The next two arms are Sagitarius, our next stop, and Perseus, about 100 million miles apart. If an extinction event is going to happen, it will likely happen in the Sagitarius arm or in 'open space' between the Orion and Sagitarius arms. While the sun is orbiting it's also 'bobbing' around the galaxy's mid-plane which takes about 70,000 years, or about 35,000 years above the plane and the same below.
A mathematician astrologer might be able to predict exactly where our solar system was on any given 10 million year increment, in which arm if any, whether the sun was below, above or on the midplane at the time of (a past or future predicted) extinction events. Just as astrologers predict where the stars were on a famous figure's birthday. Where was the earth 439, 364, 251, 214, and 65 million years ago in relation to where the earth is now? What external stresses of the space environment were the sun and earth subject to in each arm/interval between arms?