I think I can answer your question for Muslims.
------"If God doesn't exist, why there are so many people who believe God does exist?" Group psychology plays a cruicial role among the religion believers.
Assumptions! There is one fate that all will endure "Death" just like Stephen Hawkings statement of no god and no fate guess what he died fate accompli! And he wished there is nothing just like you all that this IS be all and end all! No, you hope it and you wish because for all that matters you are the ones asking if ye had known.
Qur'an says "Blessed are those who have not seen and yet believe"
because guess what if you had seen would be fate accompli ain't it?
And, again, Qur'an [2:255]
"Allah! There is no deity save Him, the Alive, the Eternal.
Neither slumber nor sleep overtaketh Him.
Unto Him belongeth whatsoever is in the heavens and whatsoever is in the earth.
Who is he that intercedeth with Him save by His leave?
He knoweth that which is in front of them and that which is behind them,
while they encompass nothing of His knowledge save what He will.
His throne includeth the heavens and the earth,
and He is never weary of preserving them.
He is the Sublime, the Tremendous."
There is yet another argument as it says in Qur'an of a person who has been Blessed with a lot of wealth because of his fruit orchards and his argument is there is no god and if there was one then he would bless him after his death just like he did here. That has been narrated in chaper 18 The Cave.