I think appearances are deceiving when it comes to that. Probably just looks that way because the camera isn't really focusing on it at ground level. If you got down really close, I bet it's disgusting like
@quietcandy mentioned about the dirty bottoms of socks.
I doubt they're having people come and clean for a couple reasons.
First, Tim and Jenn are weird about people being in their house when they're not present (you know, cuz they're ceLeBriTieS); that's why I couldn't believe when they actually left the organizers home alone for a couple hours.
Second, having people come and clean your floors would require you to pick up and move all the toys, boxes, random
tit, etc. that's piled up all over and put it somewhere and everything always looks exactly like it did before they leave vs. when they come home in the vlogs. And companies aren't going to move crap around for fear of breaking stuff and then being held liable.
And I honestly also don't even think typical scrubbing / cleaning like you do (and other normal people do!) is even on their radar to even consider doing - or hiring someone to do.