It’s so BORING.
It’s clearly a name that was picked because it was the least offensive or risky option. “Red Tails” is objectively cooler, but presumably was seen as more obscure or that it would piss off some less enlightened fans by naming the team after Black aviators. Similarly, Cleveland picked the amazingly dull Guardians over the truly ass-kicking Spiders.
If you think about it, the very best nicknames are the ones that are kind of odd or unique to the sport. Lots of leagues have team names like Lions, Hawks, and shit like that, but when I say Celtics, Packers, Penguins, or Dodgers, you know who I’m talking about. Weird names rock. These days odd names like that would never get past the committee of upper class white communications degree holders.