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

A belief in a god is not the problem.

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.

When should I use the best sunscreen for oily skin?

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 .

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

Joni Ernst Issues Non-Apology for Joke About People Dying Due to GOP Medicaid Cuts - Rolling Stone

THE BIBLE IS THE PROBLEM!

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?

Why do people always talk about Ohio as it's a dangerous city?

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

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

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

In the search for signs of life on Mars, Perseverance reaches a crucial rock site. - Farmingdale Observer

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