It's a bit funny, but it's really a question of distance more than medium.
For in-rack, DAC/Twinax is just copper and good for 400G, and cheaper than separate optics and fiber.
For in-rack, DAC/Twinax is just copper and good for 400G, and cheaper than separate optics and fiber.
DAC cables are a bit harder to route than fiber though.
And, DAC has lower latency and uses less power than 10GBASE-T (e.g., even at the lower 10Gb speed due to latency you don't want storage over 10GBASE-T).
(Not that anyone is still reading this old article or would likely care if they were)