Most left handed people do this because nearly every single tool we ever use is designed either explicitly for right handed people, or it had no hand bias at all. Right handed people never ever think about this. You never realise the extent to which things were designed for people exactly like you until you're in a situation where they're not. I always thought it would be really interesting to make left handed versions of the things left handed people struggle with (scissors, canopeners, gravy ladles, pretty much everything) and then make right handed people use them. And make them write a ten page paper by hand in a left handed desk exclusively in notebooks with the spine/rings on the right side. And see how long it takes before the right handed people lose their shit.

Left handed people would also struggle a bit with this, because we grew up with exactly the same nonexistent access to left handed tools - yeah, we hold things in a weird way, but only because we have to. But I expect we would adapt much faster and probably nearly universally have way more dexterity with our right hands than right handed people have with their left.