Also: if you have to tell me it's simple, rather than showing me examples that make it apparent, I assume it's not.
For example, Suckless Software describes many of their Linux applications as simple, and it’s a fitting description that also encodes the spartan nature of the projects compared to their more commonly used counterparts.
But outside of a README or GitHub project description, I completely agree. Simplicity is the absence of complexity, and will become in retrospect when users choose what you’ve made because you made it simple enough to do so.
But if I’m searching for e.g. a “simple monitor hardware brightness control for Mac” without extra nice-to-have features or GUIs, a project that describes itself as “simple” gives me a useful clue that the developers might have priorities that match my needs.