@Sarah977 In US everything is done by contract and legal acts, especially in real estate field. My wife is a realtor and she was specifically taught when studied for the license. Several hosts doing this doesn't mean it's legal it's just we haven't heard any tenant fight back on it. There are a couple things we need to note here.
First, if there's a leasing agreement then landlord cannot disconnect any essential service. It's usually difficult for landlord to prove if the tenant physically lives in the property. And even if the landlord can prove that, disconnecting any service is not the proper way to respond to the tenant's refusal to pay rent. Disconnecting service on purpose is a breach of the lease as well. Tenant can sue landlord for disconnecting service it's just most of time this is not worth the time/money spent on it.
Usually the lease between landlord and tenant will allow the tenant to bring in "friends". So in this case the tenant's action to bring in Airbnb guests is kind of in the grey area. The tenant is certainly breaching the lease by listing it on Airbnb, but bringing in "friends" is allowed by the lease so landlord probably cannot ask police to kick them out.
If the owner lists the property on Airbnb, when guest's booking come to an end and guest refuse to leave, that's a completely different story because as long as the length of the guest's stay doesn't reach the threshold defined in the landlord-tenant law (for example 6 months in Philadelphia), the guest is not protected by the landlord-tenant law. In that case, host can define the guest as "trespassing" and can take any action against the guest including disconnecting service, ask police to kick them out, etc.
I think Airbnb should step forward to solve this type of issue, basically by mandating that only property owner or licensed realtor can list the property on Airbnb (by name matching), and if it's the case of agreement between landlord and tenant, the tenant can be added as a co-host to manage it and landlord will distribut the money. In this way the landlord has full control and can also ensure the tenant is paying rent.