Why do so many cyclists like Dan Walker wear dark clothes making them vulnerable

I was looking at the video of poor Dan Walker being knocked off his bike. No excuse for the motorist but I noticed he was wearing very dark clothes. Just lately so many cyclists I’ve seen are dressed head to toe in dark clothes making it more difficult to see them. We used to be told to wear bright clothes, to be seen. Ok cyclists have extra Highway Code rules to protect them but don’t they realise the importance of being seen?