Why would you think a writer would spend three hours on a single paragraph when it ends up being indistinguishable from ChatGPT?
Is that an efficient use of time?
How would such a writer that spends that much time per paragraph even survive in today's competitive economy?
Because they're human writers, and don't sit down and calculate the most efficient use of time, and then only do that? Most scientists and engineers I know aren't that obsessive about how to most optimally spend their time.
"Got Milk" cost tens of thousands of dollars per word. Sometimes it's about quality not quantity.