Let's say for example you kill 1 vampire bat which gives you say, 70 creature points. When you kill the next mob, you will roll for a chance at a minor artifact. In this scenario your odds are based on having 70 creature points, which is very low. As a result you maybe have something like a 1 in 150,000 chance without any luck. Fast forward to having killed multiple creatures and now you have say, 100,000 creature points. At this point the next creature you kill may roll with odds of something like 1 in 3. Frequency comes into play in saying that you are getting better odds at getting a drop per kill when having lower creature points.