The reason is simple. Lester Dent was Doc’s creator and the primary writer, but back in the pulp days, it was standard operating procedure to publish series like Doc Savage under a “house name,” a fictitious author. That way nobody was going to object if the publisher changed writers or, as frequently happened with Doc, Dent couldn’t get an issue in. Likewise Walter Gibson wrote well over a couple of hundred Shadow novels as Maxwell Grant, with ghost writers filling in the rest (Lester Dent was one of them, contributing The Golden Vulture)
This can make identifying the real authors of particular stories or series a challenge. Street & Smith also used the Robeson house name for The Avenger pulps, but most pulp histories I’ve read credit that series to Paul Ernst. Nevertheless, people do sometimes assume it’s Lester Dent’s work (heck, before I knew about Dent I assumed Kenneth Robeson had written both).
Dent is now primarily known for Doc, but he also wrote the Gadget Man series of adventures (I haven’t read them) and some serious hardboiled fiction for Black Mask magazine. I’m glad that he’s now able to get full credit for his work on the Man of Bronze.
(Cover by James Bama, all rights with current holder).