in sociology, the phenomenon is called an "un-person" - someone who is physically there, but not socially there, as life around them pretends they're not present. The example famous from historical literature is servants in rich houses, where the served-on would have very private conversations while being served, as if nobody else was there. With them pretty much always being around it would have been impossible to have much of a private life if you treated them as a reputational danger (in the UK, for servants to spill what they hear was literal treason, which shows you the power dynamics - but also gives you an interesting angle on what "treason" really is...)

But of course homeless people are the much better example. Noting them as people, and people with dire, existential needs, people in misery and in danger, then the civility and carelessness of consumer culture in these cities qould hardly be possible. Private cponversations ould seem (and, of course, are) ridiculously superficial compared to this dire need just a meter away.

That "bubble" is a screen of an illusion that makes city life possible, in its callousness to the unseen other.