The provider has a specific set expertise that's probably better aligned with hosting this service. Since it's a revenue center for them, versus a cost center, they're better equipped to make the case to hire specialists.
The your second point - legalese is very beneficial for that. In the US at least, as long as it's not a protected (by FISA, etc..) organization breaking into your provider's systems, contract law covering compromises is a fairly well developed area.
