If atheists have a hard time selling rationality to theists there is no shortage of reasons for a believer to ignore reason.
Theists are generally given state sanctioned privileges. They find comfort in their delusions. Theists prefer employing other theists and often give each other preferential treatment.
What then is the value proposition for being an atheist? What is it that sells atheism?
"selling atheism" implies that you choose to believe based upon the outcomes of the belief rather than its truth.
That is akin to Pascal's Wager essentially, in that you decide to believe something because of inherent options and not truth.
So, selling the idea of atheism is not really applicable...whereas the rejection of the claims of theists is something that one should make based upon the evidence....more than whether one group has better cookies or not.
Choosing a religion, based upon sales points, seems to be more inline with what happens when a person chooses a fraternity/sorority in collage.
A value proposition makes more sense for non-truth based choices. In the US for example, being a theist is the path of least resistance. Being an atheist who pretends to be a theist, say, by avoiding the issue, is the second path of least resistance.
Being an atheist who fights unjust laws and practices based upon theism, is the hardest choice, as their attempts to better the world are seen by their peers as an attack upon their rights/beliefs.
If the fight gives value, sure, that can work..but, again, fighting for something you don't believe makes sense, makes no sense.
IE: What you BELIEVE should be based upon the belief itself, not what label and associated benefits it confers.
Atheism is simply the Null Hypothesis regarding the God hypothesis.
There is nothing to sell and that may be the problem.
I would argue I have an easier time to convince someone of the benefit of Secular Humanism than the neutral position of Atheism.
Try it during your next 'debate'. Identify as an Atheist, but also advocate your moral philosophy.