Also some sexual selection involves just the right kind of disadvantage. Saying "I still rule the land even though my antlers are so big it's honestly a problem." You spend to show you've got strength to spare. You can get an ass so big it proves to potential mates you can overcome setbacks
I think the "dump truck ass" is just a sign of a healthy kobold with an appropriately-thick tail and legs to the sides. Any kobolds trying to match mammalian beauty standards will be terribly malnourished.
