Retail is dying, nobody is buying or selling houses, there are the US tariff wars, more countries are buying/selling energy without buying dollars first, the UK is heading for Brexit, the Euro is heading for Brexit, Quantitive Easing has yet to come home to roost and there are plenty of bubbles.
Meanwhile, everyone has a job and tourism is booming.
I imagine the AirBnB advisors know more than me about these circumstantial factors and would not want to be doing their big sale on the wrong side of the inevitable recession/crash.
Best make hay whilst the sun shines.