Landlord gets hit from multiple sides; those who don't like that it contains "lord" which is a male term, those who don't like that landlords exist, and those who don't like that the concept of owning land exists.
I don't like that landlords exist, but that's an inordinately stupid reason to try and get rid of a word. Surely noone believes that by sensoring a word you get rid of that which the word describes.
Please don't assume this. In the southern US in the late 80s and early 90s, "landlady" was a term that was very commonly used for female "landlords". I'm not sure if it's specifically regional, though.
I once was scolded by a United Airlines flight agent at Denver when I expressed disappointment that my full-fair buisness class ticket was downgraded to coach because of an operational change. I said, perhaps a bit flippantly, "I didn't pay for a J ticket (https://en.wikipedia.org/wiki/Fare_basis_code#Booking_class) to sit in steerage."
She replied: "Sir! How dare you compare people flying coach to cattle!"
(Of course, the word "steerage" has nothing to do with cattle. We sent a Fed-Ex to United corporate telling them we didn't like being scolded and got an apology and a full refund for that flight. This was in 1998 or so. I doubt that would happen today.)
https://www.youtube.com/watch?v=MxRkHeQ7-B8
A caveat of bending over backwards to be as inclusive as possible is that sometimes you end up including people who are just plain nuts. You end up enshrining the personal problems of a handful of people into company policy.
Are you suggesting that it's "plain nuts" to be against private ownership of land?
I didn't think of that. I always thought of it as "lording over" something. As in she's the "lord of the land."
That said, a landlord and a property owner are not the same thing. Many (most?) apartment buildings are owned by one company and managed by another.
But she wouldn't be; she'd be the "lady of the land".
I think these two groups would prefer "landlord" over "proprietor" because "landlord" has a much more negative connotation and probably inspires a visceral reaction in anyone who's had a bad landlord. Only the "male" thing makes any sort of sense from a left wing POV.
I would believe the GP's second hypothesis; it's hard to imagine who else would even think to substitute "property owner" for "landlord" (it's not even accurate!)