Its pretty clear its a problem with the leather bolsters. People saying change the way you get in and out, sure that will probably help delay the issue but it doesn't change the fact KIA screwed up by choosing a garbage leather supplier.
Take it into the dealer and have them fix it, that's really the only way KIA will sort it out in the long run.
Kia describes the way they test the upholstery. Rigorous. I've brought this up before: it's in the promo book. There is no way such an assertion as "garbage leather supplier" holds up to the evidence. If it were true, we'd be having factory recalls for failed upholstery. Instead, we have these extremely few complaints on a forum that is now over six thousand members.
The evidence says that the leather (are the bolsters even leather? I don't know but guess not: "leather trim" on all Stingers means the parts we sit on, butt and back) is almost entirely up to the wear and tear. The "leatherette" holds up if anything even better than leather because it lacks the occasional weak spots that leather has.
And yes, the way people get in and out is the biggest factor/difference in how the seats wear. Nobody wants to have to change the most fundamental factor: how they move. But how they move even determines how long their joints and ligaments and cartilage are going to last, etc.
Kia's warranty on the interior covers early upholstery wear. Be prepared for a non covered incident down the road: because if you don't change something about how you enter and exit the car, it will happen again.
(Saying, "I've never experienced this with any of my other vehicles" is valid but non sequitur too: because it doesn't address the problem. If you're right and in this particular case it was material flaw, then the replacement should prove the point. But if the wear starts up again and you didn't change a thing about how you get in and out, then that shows where the problem is; and it isn't what the seats are made of or how they are made: "Min-jun", Kia's 165 lb
seat test dummy got stuffed into and removed from the seats 20K times; the equivalent of in and out of the car four times a day for 13-plus years. So he's not the problem either. The common factor here is the individual driver's MO for entering and exiting the vehicle.)