Jet2 have a £300m drawdown facility that they haven't yet had to access. TUI have indeed been fortunate to receive German government grants and loans to the tune of several billion dollars. They've also just raised over half a billion through a share offer.
I'm sure Jet2 will look to raise further funds as and when they need to, but the fact they're not at that stage yet highlights the differences in the business models of the two companies. Business such as Jet2 also focus on a more assured income - the bog-standard summer holiday in the Med. They're fortunate to not have expensive assets tied up in market segments that will be slower to recover.
For both companies, the demand is there. It's just a case of riding out the lack of forward bookings until the consumer has confidence to put some money down.