The strings only have to be unique and pronounceable to be valuable, they don't have to be uniquely pronounceable.

When scanning a list of records by eye looking for an entry or entries, it's helpful for the identifiers to be pronounceable because that allows normal people to hold more in their short term memory than they could if the strings were all gibberish and each entry ended up consuming multiple short term memory slots in the brain. Sure, there is a tiny chance of collision but that chance is still there when scanning by eye and trying to find a GUID that starts with the first few letters of the GUID you're looking for. At that point you verify you actually have the one you want. And yes, there are lots of occassions where people look at identifiers, that's why pronounceable identifiers have value.