Here are a few years of mine - most of the life of the forum. I’m surprised to see it doesn’t vary all that much. Perhaps it looks like a slight decreasing trend?
It’s a small forum. There’s only a very small growth trend in daily engaged users:
So, I have not so many users, and they seem to keep coming back. Maybe you have very many users, and most of them visit only briefly. But how many do stick around? Maybe your monthly user numbers are a better indication of how many returning users you have.
In fact we can see growth and stickiness, perhaps, by looking at both the weekly and the monthly user visits:
(Can’t show daily visits for this long a time period.)