Earlier quoted context omitted.
I would imagine Airbnb could at some point cap the number of nights you could let a place out, right? Certainly not ideal from their standpoint, of course, but manageable?
It also prevents a legal and valid use-case -- renting out your couch every night of the the year. So long as you still live in the place yourself full-time, this isn't illegal under most municipal codes.
People might lie, but there is going to be some immediate negative feedback when people find out they've rented out a couch...