I came here to say basically the same thing. The flat but slight growth to me, speaks to the health of the community. Its not like high quality "hackers"/etc are as a population growing exponentially.
But also HN is clearly not a startup and probably hasn't spent a cent on marketing.
In fact, as far as I've learned, a lot of the work here involves stopping bad actors/users rather than finding ways to get users.
I can't read the Y axis values so I can't tell.
Log-log and a fat marker, perhaps
How come? It's quite clear. Did you try downloading the image? It's a relatively big one