Brian Pern correctly identified the root cause, supply and demand, when the supply (of pilots) exceeds the demand, pay rates go down and when the demand (for pilots) exceeds the supply, then pay increases.
The mantra has for some time been, "if you don't like it, move on" and therefore the turnover of staff has been huge and the queue of people to replace those who have moved on has meant that there is no case to increase the rates of pay, so we have a situation where a cadet on qualifying nets around £1800 and pays £1200 of that to the bank leaving £600 per month for rent, beer and fags.
There are those who look back at the 1980s as the golden years, but here we are in 2021 with 1980s pay.