We don't know' is a wonderful, fulfilling, inquisitive, and terrifying answer!
A lot of ...
Humanity likes to live in a cave. It's dark, and comforting. It's home, and filled with what we know. The world outside is bright, and frightening. It's dangerous and uncertain.
Outside the cave,there's thunder and lightning. At the back of the cave is the shaman screaming and yelling that the thunder and lightning means that the gods are angry. At the front of the cave, someone is looking up at the sky, wondering 'Why does it do that'? The answer is, 'I don't know. But I want to find out!'.
To many, 'god' is not an answer.
What is over the next hill? God. How do birds fly? God. Where did we come from? God. What are the pinpricks of light in the night sky? God.
Change the answer to 'I don't know', and we can learn more. .... We have a good grasp on where humanity came from, even if the answer on how life began is still a little uncertain. As for the stars? We know what they are, how they form, and how they die.
'I don't know' has given us many of the technologies ....
Of course, big questions may never find a suitable answer. How did the universe start? Well, we have a lot of ideas, but nothing concrete. It was a mind-boggingly long time ago, after all.
Evolution is also not a 'failed theory'. It is, in fact, .....
It should also be noted that no answer we changed from 'We don't know' to 'now we know' has ever included the phrase 'and therefore there is no god'. The existence or non-existence of a god is irrelevant. Since we cannot prove that one exists, we just ignore it since we find answers anyways.
Trying to place an answer of 'We don't know, therefore god' is limiting. Very limiting to ourselves, the universe around us, and to our own curiosity and intellect.
Are you going to stay at the back of the cave, screaming that the thunder and lighting are proof that the gods are angry? Or are you going to join us in the frightening, terrifying light in order to find a new answer rather than 'We don't know'?