Cause felt protruding from underneath some of the legs here and there looks so much better. Once the damage is done there is not much you can do and adding metal plates now will create a gap and make the damage look worse. If the felt protectors are too short then you will see the damage as well because of the gap created and when it's too long it will stick out from under the legs like the pictures above. And not using any protectors will just result in more damage. I am not a fan of pincabs when they are not needed but at least they prevent any additional damage and also cover up any existing damage.