What do you believe they are basing the risk assessment on?
The fact that there is an active war in the region and Iran has stated they will attack ships (which they have). The cargo the ships are carrying is another key aspect, a spill in the area of that magnitude is an ecological disaster and incredibly costly. Based on previous scenarios, the likelihood of damage and a plethora of other factors like the disruption of traffic as we have seen, gps jamming causing navigation issues.
They are not basing it on media reporting of dangers, there is a reason oil prices are spiking. Traffic is down a ton, its over 80%.
Why are you at war again? can you tell me that?