You already said it: "it's a fairly relaxing and charming game."
My hardcore gamer friends make fun of me for playing chill games like Stardew Valley and Spiritfarer. They prefer to spend their time in high-octane, action shooters like Call of Duty or Halo, and they don't really see the point of farm sims. They get too bored, too quickly. All they ever want to play are action games.
But for someone who lives with anxiety and ADHD, games like Stardew Valley are a great way to calm down, compartmentalize, and organize my thoughts. It lets me set my own tasks and accomplish them at my own pace, and rewards me in very small ways (optimized farm yields, friendship with NPCs, etc.) There is no pressure, no need to perform to an arbitrary standard. I don't have to worry about disappointing the group, or failing a mission, or "looking like a n00b" or whatever. I just water my crops, flirt with Abigail, and go fight some slimes.
Don't get me wrong, I play a lot of different kinds of games--including first person shooters and action RPGs. I have over a thousand hours in Skyrim and Subnautica, and hundreds of hours in Halo, Resident Evil, and Doom. But I can't play them for hours at at time. There's only so much RAAAAH SHOOT IT KABOOM AUUUGH THE ENEMY IS AT OUR GATES AAAAAAH BANG BANG BANG that I can take before I start rolling my eyes.