To clarify I'm not talking about poor people living in "hotels" i.e. rooming houses, or people staying in hotels for longer than they do today because the pace of travel was slower without airlines etc. I can't think of a great example off the top of my head but I feel like this is a thing though, people genuinely *living* in a hotel, as in they have no other place of residence somewhere else they're going to be returning to.
Was this actually somewhat common, and is there a reason it was more of a thing in the past than it is today?
I know exactly what you mean, but I think the 'boarding house' concept and hotel was used interchangeably, as in this source:
"In San Francisco a century ago, five-sixths of hotel dwellers were either working class or poor, and a passable room might cost 35 cents a night ($8 in today’s currency)."
https://www.sightline.org/2012/11/14/rooming-houses-historys-affordable-quarters/
This was not only for the poor or working class, but anyone who was moving to a new city - basically America went from 20% urban to 50% between 1860 to 1920 (in raw figures 6m to 50m+), so these were both immigrants and people moving from the countryside and looking for a place to stay as they got settled. Essentially a transient population.
I also do have an impression that it seems like in movies from the 20th century there are lots of people who 'live' in hotels, but that might just be rich(er) people - no different from celebrities & tycoons, consultants, royalty today.
On a really unrelated note I remember reading a biography about a guy who left home at 11 and roomed at a 'hotel' where the only 'beds' were ropes strung across the walls, and the boys slept with their armpits over them - look up 'Victorian rope sleeping' if interested.