Because it's easy enough for a beginner to enjoy, difficult enough that it can't be mastered, and between those two extremes is a gradual, demonstrable, continuum of performance that a player can advance along via work.
So it's challenging enough to provide endless problems but simple enough that it can be enjoyed as a hobby.
Easy to play with near infinitely high skill ceiling, very rewarding to improve and there's always something to learn. It's a game that stays relevant forever unlike other things that go out of fashion.
It's a timeless masterpiece of a game that doesn't rely on modern graphics, culture or anything else but it's own beauty and complexity to stay relevant.
For the same exact reason people like any hobby. It is fun, and it is challenging. Also, it feels good to win.
Reason 1: Chess is a high value activity. It requires focus, strategy, tracking multiple potential outcomes, and is a skill with a high ceiling. Reason 2: Every chess game is different. You will never play the same game twice. Each opponent will move with their personality and you will have to respond. Like a conversation, each new word changes the direction. Each new move creates new potential, new responses, new blunders. PLEASE SEND ME FRIEND REQUEST, I JUTS WANT TO GET CONNECTED WITH MORE AND MORE CHESS LOVERS ACROSS THE WORLD.