Online multiplayer, for many games, almost seems to stem from insecurity on the developer's part. Think of how many games have a tacked-on multiplayer mode, something that has a very short shelf-life because it wasn't the main reason why people bought the game. It exists as a bullet point to justify the purchase, to extend gameplay past the core game, but many times it ends up being the weakest component. That's all you'd get by putting it in Final Fantasy XV.

These games are built as an offline experience that people would rather not rely on other people to enjoy. We have MMORPGs for that; we don't need it everywhere.