Summary: Why do you believe in God?
One way to influence others is to first be influenced by them. In other words, seek first to understand, then to be understood. Maybe I would be less frustrated if I actually knew the reasons why you believe in God. Help me understand, and in turn I will respectfully respond, and if you care to hear I will respond with the reasons why I don't believe in God.
When you ask why somebody believes in God - a question I never ask - are you looking to learn from them or about them? If you're an experienced critical thinker, you require justification before belief, and you will never get it from a believer, because there is no valid argument that ends with a sound conclusion that gods exist. I suspect you know that.
One can only come to that belief by some other means, which will be by faith, by which I mean unjustified belief. Perhaps you understand that neither of you can convince the other of anything, because you use fundamentally different means of deciding what's true. The theist will always ask you to relax your criteria, which you know better than to do, and all you can do is offer evidence and argument. If they didn't come to their theistic position using those, they won't be budged from it by them, either.
This is what I mean about not being able to learn from the theist, just as he can't learn from you. But you can learn about theists. One has already offered that he had an experience that he was sure was gods, another knows gods exist because he sees their effect on the lives of others, and another has answered that theism makes them better people and enhances their lives. Isn't that what you would expect? Others will tell you that it gives them a sense of identity and community. Whatever, it will never be a sound argument for the existence of a deity or gods, and it will never be enough for you.
False consensus is one of the cognitive biases we all suffer from, wherein we believe that other people think the way we do in the main, the difference being that some do it better and some worse, but in the end, the other guy will see reason when you present it clearly enough. If only you find the right words, surely they will see the merit to whatever it is you're arguing, because brains are more alike than different, right? If you just present it with crystal clarity in the simplest of terms, surely that will have an impact. But it doesn't.
I suspect that you know this already, but if you want your frustration level to be reduced, recognize that you will likely never succeed for the reasons I gave, and consider adjusting your goals. The discussions are still worth having, because there are people who will benefit from your words and arguments, maybe even you for putting them into words, which I always find helps me clarify my thoughts, but as long as your purpose is to break through, I predict repeated frustration.