Dog whistling. Its not about actually wanting the candidate who elocutes the most effectively, its about telling their core audience "yeah we don't think black people are capable of intelligence either, just like you"
Don't forget his presidency came off the back of W. We were all sick of hearing gibberish from the president of the united states. Everyone was happy to have an articulate man in charge
Obama was the most articulate president we've had in 50+ years. Chris Rock even did a comedy bit criticizing people who commented "he speaks so well" about Obama.