I agree. Its not just a scheduling issue. The "cloud" can move quickly and if you end up near it there can be enormous damage to the airframe not just the engines.
I was on the last aircraft out of Manilla when the local volcano went off and as well as engine damage all the windscreens and a number of pax windows had to be replaced and the air conditioning system had to be stripped down.
The associated weather can also be extreme. The associated cloud system makes it impossible to see the cloud around you until it too late.
You know you are where you shouldn't be when St Elmos fire on the windscreen is orange and the smell is putrid in the cabin. By then its too late.
Wunwing