Stretching out of shape in the middle was the big one. Two people turning over in their sleep pulls the fabric instead of sliding over it
But, it was also prone to tearing along the fitted sheet where elastic is sewn; jersey knit just doesn’t handle pressure in small areas very well.
My wife also didn’t like the way it would crease up even when she was alone in bed. I never noticed it much when I was alone, but it was a big problem for her.
It comes down to the benefit of nice , stretchy fabric also having drawbacks. It’s light, cool, and very comfortable, but it isn’t a good bedding fabric overall.
Bodies don’t actually burn well at all. Even dried out bodies more smolder (people used to burn mummies, among other really silly things they did to them) than burn.
So, you can definitely make a pyre to make sure any flesh is gone, but the zombies won’t make good fuel.