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.

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

A Mistake Led to the Discovery of an Underwater Island Full of Rare Earth Elements - The Daily Galaxy

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?

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

Is the water safe to drink in England like here in America or is it necessary to bring tablets to prevent any cholera when in London?

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!

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

Why is the French way to say please is "S'il te plaît" and not "Pour Favour" like Spanish and Portuguese "Per Favor" and Italian "Per Favore" in the Romance languages group?

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?

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.

Is there a possibility that we are living in a simulation and that there is a concept of rebirth?

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