When your flights take off you get the ticket revenue to your account (minus catering and landing fees), which improves your bank account.
The detailed flight calculation takes into account leasing charges and staff salaries. These costs are not deducted at take off, but once a week.
That’s why your bank account improves, because you don’t have to pay leasing and crew instantaneously. At the end of the week, your bank account will hold less money if your flights loose money.