here's my point, i could start a new character today from zero, do every quest, max all stats and skills, loot every possible item, get every glyph, every weapon, do everything and not once engage a single other player. yeah, it would take 10 years of realtime and it would be extremely boring, but hey, my life is overflowing with adventure, romance, and intrigue, so yeah, i want to escape to a world filled with dull, repetitive, monotonous tasks. so why make this game multiplayer? why make it online? the system doesn't call for engagement between players.
the questions you should really be asking are: Why does your character want to go out and slaughter thousands of creatures? Why does your character want to become a master armorer? Why does your character want to become a master smith or own the highest quality weapons? Why does your character want to buy stuff? Why does your character want to hunt or cook?
answer those questions and then you'll have the reasons to do those things.