The UK Govt appears to have decided that it doesn't want any more Brits to go on holiday to Spain. Boris / Rishi have seen how much bringing Thomas Cook's customers home cost in Sept 2019. Boris also knows how much hassle was involved bringing everyone home in March 2020 at the start of the lockdown. HM Govt appears to have decided it is not willing to pay to evacuate everyone back to the UK and would rather pax and airlines just sort it out themselves instead
Getting back to Jet2, what they are being criticised for is consolidating return flights, which mainly seems to mean people coming back earlier. So early return flights are available, but people don't want to use them.
What exactly are the government meant to do, send the troops in?