It wouldn't be in the lease, it's not for the tenant. Landlords will carry liability insurance for their units in case a tenant or their guest is injured, etc and decides to sue the landlord. Those liability policies often have limitations on who they'll cover, how the unit can be used, etc.
I'm guessing the insurance companies find a way to avoid covering you if you let a tenant sublet their apartment hotel-style... if for no other reason than I'd bet policies for hotels are more expensive than residences. (And hotels have to have better fire protection, etc.)
Right. I should have been clearer. Airbnb person staying in building sets building on fire. Insurance companies always look for anyway not to pay. Search web, find evidence that apartment was active on AirBnB and deny claim as it's a breach. Now everyone else in the building has to go after the Landlord directly.
Bottom line would appear to be that leases will soon specifically speak to this new business model and it probably won't be what most people would like to see.