IMO: skill issue.
Communicating effectively on camera is a learnable skill, it's not one most people in tech have. But making sure people are trained to do a good job is a management challenge and it's incumbent upon management to make sure people are doing it. If, after two years, your team still has trouble having real conversations over a teleconferencing solution? That's a management failure.
"Lunchroom conversations" are arguably the hardest thing to foment in a remote environment for sure, but between things like cross-teams with breakouts and the like, you can do it. And some people are going to do it naturally; I know what most of my director's peers' teams are up to and I have contacts in all of them, while also touching base with them on a regular basis. If your teams don't have people who do this naturally, assign it. If you don't, that too is a management failure.
"It's hard" is true, for sure. But "we decided we don't want to and never wanted to try, so we're going to inflict misery on our employees" is an abrogation of the employer's part of the social contract.