He’s a lefty
This makes you wonder about one obvious question: does he realize he’s only chewing left shoes? Is he even aware of it? This has to be completely accidental! We’ve already seen that dogs can chew anything they want, and slippers are just the tip of the iceberg, so maybe they should be thankful.
Would they prefer it if eh chewed both shoes? I’m not sure. True, even if he chews only the left one, he might have well ruined both of them, since the pair is out of use altogether, but still, it seems like it could be worse. We see a simple solution here that doesn’t involve online shaming: hide the good shoes in the closet and by a couple of pairs of cheap shoes for him to chew away.