And for what it's worth, Bill publicly broke his anonymity at his death, I have an original NYT with his death announced. Which further goes to it being to protect the alcoholic from his own ego. It was never a "secret" who Bill was, his full name was on many corporate documents that anyone could get from the NY state corporation commission, etc. And Bill never made his name a secret, he also referred to many others by their last names, particularly Hank Parkhurst, Fitz Mayo, and Jim Burwell and he referred to Dr. Bob as "Smitty."
In addition to protecting the AA from his own ego, it also safeguarded AA candidates by putting their faith in a public figure. If the public figure failed (picked-up), it reflected poorly on AA.
There is also a negative stigma on drunks. The town Doctor doesn't necessarily want it known he is in recovery. Bill W. stresed the importance of anonymity not just for the individual but for the group.