I totally get that this is irritating, however, there is also an advantage when run by someone like facebook: Users care about their existing profile and will behave better because of this (basically because they are not anonymous). IMHO, this is why FB marketplace works so nicely in the US.
Yet, most of the time, we're using usernames to hide our identity because we don't want to have our real life connected directly with internet strangers.
A sterile virtual environment ran by a company that makes money on me giving them my personal info?
Not sure I'd want that.
Plus, the fact that this is going to be a VR clone of Second Life without the anonymity and most probably without all the rated M stuff makes me rather sad. A big missed opportunity.