Line chart's Y axis not working properly

[IonuDragomir1]

Hello,

I'm testing line chart and I'm a little bit confused of the usage of Y axis setting. I don't understand why each line of a chart can get a 1 to 4 Y axis. I think that the number of Y axis should be according to number of line added to a chart. Do you agree with me?
As you can see in the below images, I have added a chart with 5 lines but only 4 Y axis were added.