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

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

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

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

Why can't I lose weight?

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

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.

Dismantling CDC’s chronic disease center ‘looks pretty devastating’ to public health experts - statnews.com

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

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

A belief in a god is not the problem.

Geologists Just Cracked Open a 500-Million-Year Mystery in the Grand Canyon — What They Found Is Rewriting Earth’s History - Indian Defence Review

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?

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

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.

What specific economic and social impacts would result if all climate change policies and regulations were immediately repealed worldwide?

THE BIBLE IS THE PROBLEM!