There seem to be at least two issues here: 1) pay and conditions relative to other options (which your example illustrates) 2) the system's inability to react

There seem to be at least two issues here: 1) pay and conditions relative to other options (which your example illustrates) 2) the system's inability to react quickly to changes in required throughput, because hiring and training takes at least a few weeks(?) I wonder what's the dominant reason for today's situation, when Heathrow worked fine before the pandemic? A) Potential workers have better options (or better information about options) than they did before the pandemic? B) The airport and airlines failed to forecast accurately enough? C) Some other type of 'bug' in the system of management? D) Something else?