I was listening to a years-old podcast chat between Joe Quesada and Kevin Smith a few weeks ago, and Quesada articulated this idea quite well when talking about his experiences launching the Marvel Knights line (and how hard he fought to keep it a relatively small, limited imprint after it took off).
He said that the notion is quite ingrained at Marvel that if an idea works and is successful, you then seek to replicate that idea on a larger scale and apply it across the line. But, he explained, in doing so you can often lose what made the idea special and made it work in the first place (either by diluting the quality or by making a novel idea almost immediately commonplace).
I get the sense that Marvel saw the success they had with one or two of these ‘diverse’ legacy characters and sought to replicate that across the line. And in doing so they fell into exactly the trap that Quesada pointed out.