Do most people not know how to fight in the opposite stance from which you're used to?

For me it naturally came to me to be able to fight southpaw whilst being right handed which I thought was normal but lots of people at my gym dont usually use southpaw (since most people are right handed) and I always see memes about fighting a southpaw and wondered why not just also switch stance and I also noticed in some kickboxing/Muay Thai and MMA fights that when someone key is being kicked out they don't switch stance for some reason. I get it's different for everyone but surely it comes to the point if realisation that Ur gonna need to be able to fight with both stances.