I don't think it going unnoticed is the problem - People know it's there, they just have no reason to click on it. Daily challenges frequently break, and many ordinary challenges are either not rewarding enough to warrant any investment of time, or usually require two people, as outcome required is a complete improbability when solo (i.e. Winning games without getting kills). Challenges such as 'True Challenge' from Tower Defence are definitely difficult and rewarding enough to encourage people to open the menu, however Tower Defence is the only gamemode on the server to actually have challenges like this, and given the uniqueness of its gameplay, it cannot appeal to everybody.