Many people who live in small apartments can and do host social gatherings. In my experience, how frequently someone hosts gatherings has more to do with their personality than the size of their living space.
Having your own studio in Manhattan puts you so far into stratospheric income (or a family heirloom rent controlled lease) that we may as well be talking about the problems of private jet owners.
I'm talking about the kind of people who have to choose between part of a shared apartment in a conveniently transit-connected part of SF/Manhattan, or their own studio/1-bedroom somewhere with low density and poor transit. Y'know, software engineers making $100k.
Ehhhhh... What? All my NYC friends are below average in income. None are software engineers and of course they all rent. Their housing costs are probably a very significant part of their income as well, but I've seen a lot of higher income people do the same with McMansions. A few ended up moving to Brooklyn too for cheaper rent.
I don't live in the NY metro area but I visit several times a year since I got friends there. I always crash on the couch.
I vary rarely socialize with people with high income because, one, I grew up poor so most of my childhood friends are still below average in income but more importantly I find it very difficult to relate to people who grew up well off. Sometimes I hear my co-workers talk and I feel I am living on a different planet.
As far as shared housing, yes, 99% of college kids live in shared housing and the vast majority of them still socialize.