I repeat, ask a Jet 2 guy!
Suppose he lives in Leeds and wants to work there too. The alternative is maybe to work for EZY out of Dortmund. As well as the time and effort needed to get home, it's a huge expense.
Taking into account tax that you don't have to pay, the £20k works out at £11.9k net - as small price to pay for not having to go to Dortmund for several years.
Yes, Channex/Jet2 might go bust but then so might anybody. And at least there aren't a frightening number of glossy new aircraft on huge leases just waiting to drag the company under when the downturn inevitably arrives.