Answer:
there was no data available for those numbers
Step-by-step explanation:
if you want to graph at intervals of (for example) 15, but your numbers are ranging from 115 - 200, you don't want to a huge blank space from 0 - 115 on the y-axis.
if you create a break at the bottom (and only the bottom) you can start at 100 and have intervals of 15 from there. this eliminates dead space on a graph.