I always imagined that carpets were much cleaner in the SH universe than they are in the real world, and that's the reason they're basically everywhere. We know there's nanotech in the SH universe, so I kinda thought that maybe someone figured out a way to use it to keep carpets clean. But different than how nanotech is used to keep windows clean in the real world, because you'd just have wet carpet. Given how we've seen nanotech is used in this universe, it's probably something like tiny replicating robots eating filth. Which is like a ticking time bomb if I'm being honest. But Imma be real with you, there are all sorts of ticking time bombs in this world. Don't worry about them, because they'll probably never come into play in this story.