Because they provide a reasonable simulation of the world that my character lives in ? Once more, the devs' own words: "To play D&D, and to play it well, you don’t need to read all the rules, memorize every detail of the game, or master the fine art of rolling funny looking dice. None of those things have any bearing on what’s best about the game."
Gonna beat the same drum across threads, now?
Not at all, it's just called roleplaying, which is the actual intent of the game.
The game, being non-sentient, has no intent. The game is a tool, and has goals in the same way a hammer, a chunk of metal on a stick, has goals. The intent of the game is the intent of those sitting down to play.
You may argue that the players are, or are not, using a system that serves their intent well, but that's a separate argument.