With everybody holed up in their homes all day long these days, and what with the OCD household maintenance that goes along with this cocooning behavior, it's tough to carry out a normal guest-host relationship if the guest will be staying over.
As a guest, you feel like every choice you make causes a disruption to their OCD routine, so you feel out of place and in a hostile environment. Just the opposite of how guests should feel. And hosts, instead of enjoying some new company and a brief shaking up of their routine, are more in damage control mode, trying to look out for and clean up after the "mistakes" that the guests have made -- as inconspicuously and as inoffensively as possible, of course. They wouldn't want to be rude. So they hardly feel at ease either.
Aside from the OCD stuff, the sheer amount of time that people spend in the domestic sphere these days makes it much more likely that guests and hosts will get on each other's nerves. When everyone's more outgoing, perhaps not all of the individuals will even be in the house at the same time. Or maybe they're setting off as a group to go do something fun for most of the day, and treating the home as a place to crash and recuperate after all the excitement.
Unfortunately, it's not just the fault of the hosts but of the guests too. It's not only the hosts who treat the guests as a threat to the OCD maintenance of the household, but the guests who view their hosting household as a disruption to what they're used to back in their own OCD-governed household. "How can our hosts possibly do things this way? It just doesn't make any sense! We have to get them to change, at least while we're here. I mean, it's their duty as hosts."
Just as there's no greater slap in the face as a guest to be treated like a source of uncleanliness and disruption, there's no greater disrespect toward the hosts than to bristle at how things are done in the hosting household, questioning the hosts' sanity, intelligence, purity, and so on. Right when you arrive as guests, you spray down the hosting household and quarantine yourselves from their unclean and incorrect way of living.
Houseguests and their hosts don't just let things go and not worry about what the proper way to do things is going to be. It should be more informal, but instead it's highly formal, distant, and obsessed with what's proper -- the only open question is whose determination will lead to their own OCD routine becoming established for the duration of the stay.
In my experience and observation, Baby Boomers seem to behave the best as guests and hosts -- it's a fairly grown-up thing to be doing, and they had the most experience as adults during the rising-crime period when guest-host relationships were at their peak (hitch-hiking being another one).
Gen X only started to live in their own places, and so could only begin acting as hosts, during the '90s, when the culture had already changed direction. Same with Gen Y. At least both of those generations had some experience with houseguest relationships when they were young, during sleepovers. For example, there were times when I'd spend 3 to 5 days over at my best friend's house during the summer between 4th and 5th grade. (Much of that time was spent outside or away from home, though -- and out of his parents' hair, returning to an earlier point.) He even invited me to a weekend sleepover at his uncle's place. Communal ties were so extensive back then.
Nevertheless, Gen X and Gen Y are still pretty inexperienced as adults, at best feeling awkward and unsure, and at worst are as I described earlier. The sleepover experience only protects them against behaving like total brats. A decent fraction behave all right, I'm talking as always about averages.
Millennials didn't even have extensive sleepover experience as children, so they're even less able to act as house-guests or hosts. Sheltered from social interaction during the critical period of primary and secondary school, they've ended up selfish and bratty as young adults. They're presumptuously demanding and intrusive as guests, and egotistically territorial as hosts. Avoid at all costs.
The houseguest culture seems to have been pretty minimal during the cocooning mid-century, after having been more common and unremarkable during the Jazz Age (The Great Gatsby has Jordan Baker staying over at the Buchanans', and Klipspringer the piano player at Gatsby's). If the society has gone through a full cycle before, we can do it again.