Why do some religous people..?

Make smart *** commets such as: "Just because you can't see gravity doesn't mean it doesn't exist and your just going to float into space, so not believing in god doesn't mean he does not exist and your not going to hell for not believing in him." To me they are just comparing something that has been proven to exist to something that hasntbeen proven to exist. It's like me saying that just bcause I can't see oxygen that it doesn't exist and just because I don't see Xanathar the all powerful that he doest exist. So with that kindof reasoning I guess Xanathar the all powerful exists? Hell I might just start using this kind of reasoning.