Because all of it seems like fairy tales to me. Also I don't understand why god is praised as good and merciful. For me he seems like an evil monster. Asking for sacrifices? Check. Making floods that kills many innocent animals and humans? check. Blaming people for his own evil deeds? check...Being scared that humans working together will reach the heavens? Check. This being seems not only evil but also pitiful. It has all the shortcomings of a lowly human tyrant. But no one blames it for it's actions. We blame people like Putin, Stalin or Hitler for mass killing, torture and destruction. But somehow a being who invents a place of eternal torture is praised as good...That makes no sense to me.
I don't believe that a supreme creator would care if his creations worships him. If god created me he created me the way I am. That means that I don't believe in god because he did not want me to believe in him. So if someone is to blame for me not believing is god himself. Also all powerful, all knowing being should be able to end all suffering. If it cares about it's creations. The fact that suffering exist means that either god is not all powerful, doesn't care about us, is evil or simply doesn't exist.
Another reason I don't trust religion is because it paints humans as superior beings to other creatures. god being humanoid seems too convenient. Earth is a tiny piece of dust in the entire universe. So why supreme creator would have any resemblance to us? For me it seems like human superiority agenda. god should be able to be anything. Dog, spaghetti monster, phoenix...I would find any other non-human form more believable.
I don't believe in power of a prayer. Firstly I don't believe in gods. And if I would believe in gods I would have no reason to think that they care about humanity. Existence of gods , souls or heaven seems to be just a wishful thinking and nothing else. I would not want to live forever even if it was real.