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

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

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

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

Why acetaminophen works: New discovery ends longstanding mystery - Medical Xpress

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?

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.

Making a Diving Catch For Space - NASA Watch

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

A belief in a god is not the problem.

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

What is the process of becoming an Evangelical preacher? Is attending seminary school necessary? How long does it typically take? Is it financially challenging?

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

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.

Why do most atheists in debates with theists take Bible verses out of context much of the time? Are they lying maliciously or do they not understand theology enough to understand the meaning?

THE BIBLE IS THE PROBLEM!