This is like saying people shouldn't need to be trained for a job.
There's no reason to expect a general purpose model to know what you want when you've not given it any training in what to do for your specific case.
And in this case, the models do far better than humans: Most humans can't just switch to copy arbitrary tone, just by giving them a page worth of text. We don't even need to actually train/fine-tune these models further - we just need to actually fully specify the task we give them to get them to write well.
There's no reason to expect a general purpose model to know what you want when you've not given it any training in what to do for your specific case.
And in this case, the models do far better than humans: Most humans can't just switch to copy arbitrary tone, just by giving them a page worth of text. We don't even need to actually train/fine-tune these models further - we just need to actually fully specify the task we give them to get them to write well.