The problem here is that there is no quantified scale of risk and response associated with volcanic events. We have an ever-improving ability to monitor and detect atmospheric anomalies such as volcanic residue, but we don't have a recognised methodology for determining a factored 'safe' suspension of contaminants in the atmosphere. At the moment, because we have ancient and now demonstrably inadequate rules, the mantra is 'any volcanic dust, don't fly'. But that rule was instigated at a time when our only reliable way of detecting such residue was visual - so, if it could be seen, it was relatively simple and not too disruptive to apply a defined 'avoid' area, which included a buffer zone 'just in case'. That worked fine, and the many hundreds of volcanic eruptions where that rule has been applied and followed have not caused us more than temporary inconvenience.
Now we have a situation where we can not only see far more of the stuff, but we can use very powerful computers to estimate, extrapolate and give 'worst case' projections - to which we then apply the 'any dust, don't fly' rule. As we are beginning to realise, the regulatory tools just aren't up to the job. In tandem with our improved detection and prediction techniques, we need - and very quickly - a comprehensive analysis of what is safe, what is 'safe enough (but possibly expensive in engineering terms)', what is marginal, and what is a definite 'no go'.
Without that comprehensively revised regulatory matrix, we are stuck with VAACs saying 'there's potentially dust EVERYWHERE', rules that say 'you can't fly', and politicians unwilling to put their careers on the line to make some kind of pragmatic decision. In the meantime, economies, airlines, importers and exporters, and many millions of peoples occupations, go to the wall.
Safety is not an static absolute. It is always a dynamic compromise. It's time a few politicians woke up to that.