Given the massive slump in business activity, one might wonder what they are hauling with such haste... can't be only PPE...
Regardless of the number of “dedicated” freighters in operation, a significant amount of capacity has been removed by the reduction of “hold cargo” on normal passenger flights.
As the normal amount of pax flights is reduced but people still need to eat/drink/do their daily stuff the more dedicated freighters will be chartered to haul the necessities (or fill the shortfall).
In some sectors - on-line retail, for example - there has been an increase in business volumes as people find alternative ways to survive. One U.K. delivery company would normally have circa 400,000 parcels through their system per night at this time of year. Last week on an average night they had 1.2 million.