It's like Little Mix compared to, I dunno, Fleetwood Mac.
Yeah, they're both music, but one is more popular than the other despite being objectively technically worse because of the tropes and mechanisms used to construct it.
So like lots of pop music being popular rather than actually good, Stephen King is also popular rather than being actually good. He's a product of amplification through media, and so be it - it's the world we live in. If you are mediocre but tap into a formula that works and people want to buy it, good on you.
For me, I find him actually unreadable, but I can see why others like it, as the books are paint-by-numbers and easy to follow.