Local knowledge (either your own or consulting others), recon rides, studying the roadbook, going at a speed that enables you to react to changing conditions on the road. Mikel Bizkarra posted about it; Pello Bilbao said that he knew that that corner was coming up and the speed they were going was potentially dangerous, so he hung back. Bilbao is a guy who is known for some great and high-speed descending, so maybe when you see a guy like that - racing on his home roads - taking precautions, it might be a hint that there's a reason for that coming up. Matteo Sobrero was right up alongside Rogla at the time and said that there was nothing out of the ordinary about that corner and it was just something that could happen on any road at any time. Away from those who were there or who have the local knowledge, Lilian Calmejane has raised that the bikes, the modern 'finishing bottles' and rider attitudes need to be discussed as they're causing crashes, and Mathieu van der Poel has said that the biggest danger is the riders, not the courses.
But some people who have signage to sell and a populist fanboy shill who tried to hide that he was being paid by the team whose leader crashed out yesterday somehow managed to warn everybody about the dangers of this particular corner before the route of the race was even announced, and Twitter only understands the language of outrage, so they sell that it's all the race organisers' fault.