>>7807338Because, unlike fallout 3 and 4, your choices actually matter and will impact the characters around you, factions, and the overall ending. If you’re like me you can clock in well over 500 hours on the game and still not get bored of exploring every crevice in the Mojave.
Also the DLC, save for the courier’s stash and whatnot, are basically full expansions with their own new items, quest lines, and maps to add to the game.