This picture is rather stupid.
My reason for not believing in Allah as Muslims understand him, or in Vishnu, or in Thor, is because these gods did not incarnate and die for my sin, and through their resurrection from the dead secure my own resurrection to a restored and immortal body.
Many Christians become atheists, I think, because they try to think of God outside of the revelation of Jesus Christ. God in the abstract may be more or less the same across various religious traditions. But the unique revelation of God in Jesus Christ, the crucified God who dies for our sins, surpasses them all and distinguishes itself by virtue of its depiction of God: fundamentally concerned for the good of the whole creation, he doesn't stand far off in the face of our sufferings or evils, or promise a reward in an uncertain afterlife for which we have no compelling evidence, but he condescends to suffer them himself, and to take them head-on. And through his resurrection appearances, he shows us that his victory over death and evil is definitive, and he assures it to us, also.
Christians ought to think about God as Christians, not as Muslims or Jews or as polytheists or atheists.
Addendum: It goes without mentioning that there might also be positive reasons to believe in God, even if there are reasons not to believe in him. There are reasons pro and contra belief in just about anything that matters. Not all life is so black and white and simple as this meme-for-dummies would have us believe.