As others have speculated in this thread, I think their chief concern was implicitly acknowledging that their hosts were "hotels" or whatever other business type is covered by the tax.
For one thing, making this determination jurisdiction-by-jurisdiction is much harder than simply looking up the hotel tax rate. For another, if Airbnb is representing a host as a "hotel" by charging the tax, they might be liable if that host turns out to not follow any of what must be dozens of legal requirements, again, all of which are going to vary greatly by jurisdiction.
For one thing, making this determination jurisdiction-by-jurisdiction is much harder than simply looking up the hotel tax rate. For another, if Airbnb is representing a host as a "hotel" by charging the tax, they might be liable if that host turns out to not follow any of what must be dozens of legal requirements, again, all of which are going to vary greatly by jurisdiction.