People need to be discontent with the old OS before even considering switching. It's the same with everything really, even if their OS is somehow slightly better, it wont be that much better so that it's worthwhile to go through to hassle of switching over.
That being said, Samsung phones are still going to be bought regardless, and I'm not sure how much of a decline in phone sales they would see if the OS wasn't all that great compared to android or iOS.
Kinda comes down to it's not worth for them, but it won't kill them if they do.