I think that some underestimate the chaos that the unpredictable situation is creating for airlines (and their pax). Situation is critical for European airlines which are potentially bankrupt. It is just impossible to predict when the situation will return to normal at most European airports (except for some southern ones). Just in Hong Kong there are well over 100,000 pax waiting for their flights to Europe (I am one of them) and a few thousand more every day. CDG & FRA are reopening today but unsure whether any plane will encounter some technical problems or whether the cloud will change (could be new eruptions). No way that they can all be given confirmed seats for departure in the next few days and the situation change daily, so managing by status, assigning seats, etc.. is a futile exercise. Some pax have numerous bookings on several airlines, just in case; some are wondering whether to cancel the trip alltogether; just unmanageable. And some pax are in much direr needs than others whatever their status. Asking pax to come to the airport next day just in case could work the first day or two, but now airlines have accumulated thousands of stranded pax to each destination.
A colleague of mine due to depart on monday to LHR was reassigned by CX on a May 14 flight. At least he has a confirmed seat. If the situation improves then some seats will become available on earlier flights. But the situation could worsen again as volcano eruptions can come in series.