Well, we're mostly talking about PFAs here. Those are used in many industrial processes. So they're often in products where no one actually want them. But some machine during manufacturing used them hence they're there. Not much, but because they're extremely stable and "not much" can accumulate over a human's lifetime.

As far as I understand it, they're mostly used because they're hydrophobic. I.e. prevent water from sticking. Hence if you want to buy a product that's meant to contain some PFAs, you'll find them in stuff like ski wax and anti-fogging sprays for glasses.