The third-party doctrine "proper" is about third parties voluntarily giving information to the government, which the government would otherwise have needed a warrant to get. For example, the government could effectively conduct dragnet surveillance of cell-phone records without a warrant if a mobile-phone company chooses to enter into a commercial data-selling agreement with the government: for $x/record, we'll send you all the call data. This has historically been held to just be a voluntary transaction between parties, so doesn't implicate the 4th amendment.

The hotel case you mentioned doesn't seem to involve that; in this case, the hotel is opposing the request, so there's an adversarial posture between the third-party data holder and the government over handing over the data.

It's true that in Smith v. Maryland "[t]he police did not get a warrant or court order before having the pen register installed", so the original case was a voluntary disclosure in that sense. But installing pen registers isn't voluntary at all these days:

https://en.wikipedia.org/wiki/Pen_register#Pen_Register_Act

So it's reasonable to speak of the third party doctrine being applied to compelled data disclosures, not just voluntary ones.