Why would the writing be on the wall for Apple's walled garden??
It's Apple's platform, they developed it, marketed it and took every associated risk with it.
It's Apple's walled Garden and no one forces people to buy into the platform.
If you don't like walled gardens you don't buy Apple products. It is not a monopoly. There are competing products you can buy that serve the same purpose.
I guess you'll have to ask the lawmakers in SK and elsewhere for the specifics. To me it boils down to how much influence Apple and Google have over the entire fucking world's communication etc. To reduce this to "they own it, they can do whatever" is way too simplistic and ignorant. Once you get to a certain level, there is no free market, or competition. These companies simply buy anything and everything that might threaten them, and you'd need trillions of your own to truly challenge any of it. The lock-in at this level is purposely making it effectively impossible to move from platform to another.
Like the judge says in the ruling, Apple's going to do fuck all consumer friendly decisions if it loses them money... unless legally forced to. And trust me, they will be. Maybe not in the US first, though.