Why is Dwarf Fortress so difficult?

I'm genuinely curious, why do people say that Dwarf Fortress is so challenging? Is it the complex gameplay mechanics, the steep learning curve, or something else entirely? I've heard it's a game that demands a lot of attention to detail and strategic thinking, but I'm wondering if there's more to it than that. I'd love to hear from someone who's played it extensively and can give me a detailed breakdown of what makes this game so difficult to master.