Oh, I don't know, maybe because every host on the planet will "share" their room/apartment/house at exhoribtant nightly rates in lieu of renting by the month, which leads to housing shortages for people who need a place to live vs. those who are going to visit X part of the world for a few days.

The Airbnb-ification of the world is decidedly interesting for owners, while for everyone else an added hardship whether or not you use the service.