They've 185m in cash / investments. An average negative rate of just 0.1% is 185,000
They'll have increased bad debts this year due to Covid, but a negative return on cash definitely doesn't help.
So they €1 fee per transaction might off set the loss or a very small return on any investments they hold.
If they set a smaller account balance and returned some of the cash it may reduce the loss making on negative returns