You see, the problem with running an illegal human clinical trial is that the rest of the medical community tends to frown on that... and they also tend to revoke your medical license too.
While still technically having a Ph.D., after losing his license, the news channels probably didn't want to give him the honorific of calling him a doctor. Also, continuously referring to him as "Doctor William I. Roberts" probably got repetitive... "
Bill Roberts" or "Ink" would seem easier for news anchors to say and also easier for them to paint as sinister.
It's also possible that they weren't allowed to call him "Doctor" in news casts. The medical licensing board of California may have weighed in on that and made the request. (After all, we only heard one tiny segment of one news report.)