Hint: This has nothing to do with a zero y-axis, why would one need to have a zero value to have the y-axis start at zero?

The reason to have a non-zero y-axis for time series is to amplify changes, e.g. the changes might be to small to see with a zeroed y-axis. Or you have ups and downs and want to compare them, with a zeroed y-axis again the changes might be too small to compare.

Whenever you want to show growth, a non-zero y-axis is usually a sign that the aim is to overstate growth, because we as humans estimate growth by the steepness of the graph, not by the numbers. A non-zero y-axis creates a much steeper graph and thus growth is perceived much higher than it is.