There's pretty much no spare freight capacity at all anywhere in the world at the moment, I noticed a Belarus reg'd IL62 operating into Doncaster the other day - one of the last civilian type operating in the world I think!
Aircraft need to move sheer volumes of freight at the moment rather than weight. If you think about strapping a load of PPE to airliner seats, you can't really fit that much in the cabin of them compared to a dedicated freighter.