Could it be that when the seats are being assembled someone is missing installing the upholstery hog (the name for that metal clamp) for that portion of the seat?
I replaced a cover on my 2014 myself and wherever the seams were there we spaced for hogs to go that you had to clamp to a metal bar embedded into the seat. If those hogs were there the seam wouldn't bubble up like that.
Edit: NVM, I took a look at the picture posted by Anchorman and there's no where to clip anything to for where that seam is. I wonder if that's the issue as the old seats had clamps along each line of stitching.
I actually volunteer with a rescue group and one of the cats we were fostering peed in it's carrier while I was transporting it and it got into the passenger side rear seat cover and smelled horrendous. I but the bullet and bought a new cover and reinstalled it myself to get rid of the smell.
I have a 2015 CX5 Touring with 42,000 miles, and my cloth seats are pristine, and I am 6'2", and weigh 270 lbs. The trouble with natural leather is that it stretches. I have had a couple of cars with good Naugahyde, and they held up very well. Of course Naugas are getting hard to find anymore, so their hyde is rare, and expensive.