It takes practice, like anything. I work with some people who I know know their stuff, but because they never have any need to explain it to people who aren't also experts they are terrible at explaining what they're doing to non-experts.

That said, there definitely are people who hide that they don't know what they're talking about in a bunch of jargon. I work with some of those. They use the jargon to convince people who know nothing about a topic that they know something in an attempt to climb up the totem pole.

I've spent much of my career explaining things to people who aren't experts, so that is something I'm pretty good at, at least in comparison to others I work with. Though I work with a PhD geologist who's an absolute master at it, and it's a joy listening to him explain stuff. But he's from an older breed of academic who took that as a source of pride.