Yeah, you can technically extract your own keys from your own Switch, and (at least with current laws and court precedents) that would be legal. But extracting the keys requires hacking your Switch, which either requires an early generation Switch (early Switch models have an unpatchable exploit that allows them to be hacked via the USB-C and MicroSD ports,) or installing a modchip in newer/current Switch models. And that’s probably more involved than you’d like to be.

There’s also the whole issue with Lockpick (the homebrew utility used to actually extract the keys from a hacked Switch and dump them onto the MicroSD card,) being taken down by Nintendo months ago. So even if you tried to get the keys in a more legit way, you’d still need to visit some sketchy sites just to get the Lockpick homebrew. This is also how you could acquire the firmware files in a legit way. You can just extract the files directly from your Switch.

But that’s a lot of extra effort (and a lot of potential for bricking your Switch when trying to install a modchip) when you can just download all the necessary files.

I’m pretty sure the only difference would be that people with a jailbroken switch can extract prod.keys from it. But afaik most of the tools people made to assist with that got obliterated so I don’t think it’s worth doing for most people.