First I didn't forget about Isaiah Bradley. He is the result of one of those retcons and never actually took up the mantle in an official run of the book (coincidently, if they were going to give the mantle of Captain America off to someone so they could have a black Captain America, Isaiah Bradley given a rejuvenated body or Eli/Patriot would have been better in my opinion).
And God of Thunder is the mantle that Thor possesses. If she would have taken on the role of Goddess of Thunder or Protector of Midgard, we would be having a very different conversation. For example, Victor Alverez calls himself Power Man, a name originally made famous by Eric Josten (Goliath/Atlas) and later by Luke Cage. Luke Cage currently goes by his own name now. What is going on right now is the equivalent of Victor deciding to call himself Luke and the real Luke said sure, I'll just call myself Cage. It doesn't make sense.
And yes, you are right, Marvel has tried passing on the name of Thor to others. It didn't work. Dargo appeared as Thor in one story on his own and popped up for Thor Corps. Red Norvell never headlined Thor's book. Eric Masterson was killed off. There is nothing original about this character or the concept. As stated they have replaced Thor before. There is even a what-if story where Jane took Mjolnir, thus making Thor a female. Earth-X had Thor transmuted into a female. Even the costume is a knock off of old King Thor, cut for a female and given Eric Masterson's helmet. And she is an environmentalist type a la Ultimate Thor.
You ask why sales are still pretty high for Thor comics right now? Its because Aaron is a coward and is keeping Thor in the book so hard core Thor fans are still reading it because Thor is still there. If Thor was removed and all you had was female Thor in it, I'm willing to bet that number would fall. If Thor began appearing in another comic, say Journey into Mystery, I'm willing to bet you would really see that number fall. Even people who adamantly defend this whole thing like @ms-lola say that the story is weak and they are holding out hope it gets better because they like and believe in the concept.
There are so many ways that Aaron could have done this without breaking faith with Thor fans. He choose not only to ignore, but antagonize them.