It is probably because travel will take a lot longer to come back than most of us expect. This is because travel is probably one of the prime ways covid-19 can start spreading again and governments will be very leery of any activity that will restart the spread.
I bet travel will be restricted till there is a vaccine yet no vaccine is in sight. Perhaps in the meantime you will be forced to take a covid-19 test before boarding and when you come back?
So you should expect AirBnB to lose virtually all its business till major tourist centers and sources of tourism have stabilized. And you should expect that it won't come close to recovering till there is a vaccine.
Then you have to add on that travel is discretionary and given the economic shock, travel will be the first to fall and last to recover.
So months to recovering some and then no full recovery till a vaccine is found (> 6 months to year(s)). One good proxy is the Olympics. It's been postponed to July of next year.
I bet their burn rate with ~12000 employees is >>1B per year.