I imagine most people just don’t really know which style they’d prefer until they’ve already gotten used to the default right-handed method and don’t feel like starting over. Non-standard play also makes it harder to find an instrument, and learn chord finger positions and online tabs, as others have mentioned.
Growing up my family only had one pair of scissors, and they had a big, bulky plastic handle that was curved specifically for right-hand use. It was the most uncomfortable thing to use, and my parents refused to buy a second set of scissors when the one we had was “perfectly usable.” Please, buy your lefty kid some scissors that don’t dig into their skin when they try to force their fingers into the handles backwards.