That's not always true. On my most recent cruise aboard the Treasure, the tables were very close together and the guy at the table next to ours never stopped complaining about it. But on the cruise before that one, aboard the Wish, we had a fantastically private table for two! There weren't any other tables right next to ours in any of the restaurants and we had a great view of the stage for the Frozen dinner show.
Besides, there's more to a private table than just space. I don't want to share my bread with forced tablemates. I don't want to have to order and eat on their schedule. I don't want to talk to them. A private table, even if it's right next to another table, prevents those things from happening.
