A fake item in a slab can't be inspected. A fake slab can be made. The authentication can be forged. In other words, the claim that a slabbed item provides some sort of security is totally false.

So I guess the next step is slabbing the slabs, so we can make sure they are not copies?

I will revert to my most basic personal reason for not wanting anything in a slab. I collect for my personal pleasure, being able to handle and admire what I own is part of that.