The problem for seated events is variations on, four people buy tickets together, seats ABCD, and the people in seats B and D drop out. They have friends who would buy the empty seats, but instead end up with a stranger in between them.

Or two people buy seats together, one can’t make it, and now the other person is stuck sitting with a stranger. And they have a friend who also wants to go who is also sitting alone.

The venue might still sell out but it’s a worse experience for everyone. Even groups who all get in together get annoyed by people trying to swap seats or cram in the aisles to be with their friends. Venue staff are stuck dealing with crowd control issues.