It is a valid point and a good analogy that the complexity of the world needed someone to put it together. But still is no evidence that someone actually did. We are not dealing with inert mobile phone parts when we talk about the world. We are talking about living, changing and growing pieces. The rate of chance that things just came together to work, is dramatically increased when there are parts that can alter. I do not suppose to know why they are in existence in the first place, as no scientist would either. But to fill the gap of knowledge with the idea of a God is a rather big unfounded leap. We prefer to admit that we do not know yet, which is the beauty of science, instead of proposing to explain something with no physical evidence to back it.