It's not unknown that once a major airport is closed by a sudden incident, both routings to and capacity at the diversion point can rapidly diminish and cause difficulty to anyone who held for a good while.
Delta had a comparable incident (without the repeated need to emphasise their situation) back in the 1990s, with I believe an MD-11, where London Gatwick was obstructed, it held for quite a time until they had to divert to Manchester, for which they then got a non-optimum flight level and extended track, and then congestion approaching Manchester. They were actually offered Liverpool as a straight-in option. I think there was an AAIB report.