Oakland's defense was 22nd and 26th in Norton's two full seasons there -- albeit with less talent and a different scheme than Seattle's -- and it wasn't faring any better when he was fired in November.
In the absence of an explanation from Carroll, we can take only educated guesses as to why he's essentially redoing his 2015 decision to promote Richard over Norton.
In fact, it's believed that endorsements from Sherman, Thomas and Kam Chancellor helped tip the scales in Richard's favor when Seattle promoted him from defensive backs coach to defensive coordinator in 2015.
Richard played a hands-on role in grooming those players into stars.
That suggested a deal was still possible even though Kaepernick left Seattle without signing.