Well, it does make sense, doesn't it?
What we're interested in is not the number of users, but the trends: whether the number is increasing or decreasing over time. Starting the axis at 0 would not be useful in this regard, as the trend would be almost completely obscured.
At some point recognisability is also worth something. I can immediately read this graph, I understand it, it's good.
Occasionally it's used in a confusing way where people assume it starts at zero despite it not being the case, and sometimes intentionally so. But that's just the case here.