There are so many clans in this day and age that in order to get people (especially random people) to join, you really have to do something that makes your clan stand out. People have to look at your clan, look at the other clans available, and say "This guy's clan offers more than these others.".
Basically, what does your clan do differently than all the other clans? What are the benefits to joining your clan and not someone elses? Remember, you're competing against like thousands of other clans, so you have to do or say something that makes people want to join yours above other players.
Additionally, many people don't use the Elite Website or Elite App, and thus don't even know they have invites available.