There is no "must" as there is no regulation dictating such a requirement in the US. UA's policies suggest a hotel should be provided when it is their fault for the overnight delay. Technically they could make the argument the weather/ATC delays led to a timeout, but usually a crew time out they will consider UA caused even if it was weather that led to the issue. That being said, the amount of disruption at EWR last night, whether there was even any reasonable hotels available at the point the flight became an overnight delay is a completely different question.