Why does it matter so much to atheists that God doesn't exist?

I am speaking to the US Bible thumpers here, of course ~ many of whom are flat-earthers who deny evolution and see scientists as evil people who are constantly trying, and succeeding, in disproving their beliefs one by one.

THE BIBLE IS THE PROBLEM!

A belief in a god is not the problem.

5 health issues that can occur due to Vitamin D deficiency - Times of India

And then use and ENJOY these fantastic scientific advancements every single day of your life?

These are man made rules - made thousands of years ago for the use of the humans who lived thousands of years ago.

Because these are not any gods rules we are talking about.

Why cant I breathe when I sleep on my back, I can breathe if im on my side or stomach but I feel uncomfortable since either my neck is twisted or my back is in pain, im physically healthy and my surroundings are clean so whats the problem?

My problem is that people who try to shove their rules down everyone's throats - including by physical force - DO EXIST .

I do not personally care if you believe in a god or not.

IT does not matter, mainly because it does not exist.

What is the reason behind some people wearing trunks instead of speedos when swimming in pools?

The people of the modern world have evolved past all of that nonsense.

And how do you deny hundreds of years of advancement in all fields of science?

Those rules that you are trying to reinstate are rules made by men who didn't know anything about the earth, nor anything about all of the other inhabitants of it. How can you not see that?

What methods do private investigators use to investigate someone in real life?

Notice that I said their rules, not any gods rules.