Firstly, in many cultures, people were forced to write with the right time up till the 1970s.p (https://en.wikipedia.org/wiki/Bias_against_left-handed_peopl...)

Also, when left-handed writing became accepted, there were special left handed pens (with a broader tip that you can push forward without it ‘biting’ into the paper)

Finally, how do you know nobody did that, and got harassed for writing incorrectly?

Left-handedness is somewhat associated with mirror writing (https://pmc.ncbi.nlm.nih.gov/articles/PMC2117809/:

“Particularly when produced spontaneously, mirror writing is a highly heterogeneous phenomenon: the mirroring may range from as small an item as a single reversed letter, through numerous reversed letters but not words, to thousands of pages of mirrored script; the place in the word in which a mirror letter occurs is variable, and numerals may or may not be reversed too”