There might be something the cat deems dirty on the floor and so is trying to cover it up. Just this morning one of my cats had a piece of stuck poop fall off her long fur. My other cat scratched the (bare) floor around the poop to cover it.
My cat Mooshoo scratches the bare floor sometimes- not anywhere near her food or litter box, or if she's up on a higher surface she does that. I think it might be some scent leaving, or exercising claws to shed the claw sheath (I read that when I looked it up.) Waffles doesn't do that at all.
Feeby has done that from time to time, and usually when she hasn't bothered to scratch inside the box. But, still no rhyme or reason to me because she also rarely scratches (covers her stuff) inside the box either.
Maybe trying to get litter off their paws? Place a rug there, and see how much litter is collected on it over the course of a day or two. You might learn to appreciate them doing it, even if you don't know exactly why!!
Sandwich is I swear shes OCD she doesn't stop covering until she feels it's good and covered and the litter box is in a bin so she scratches that it drives me nuts when I'm trying to clean her box and she doesn't stop I have to pull her out of the box so I can change her litter spooky on the other hand just s scratches she doesn't cover I don't get it