It is a business decision by Carsten Spohr to not refund anything at the moment.
The Lufthansa Group is holding onto that money so they can effectively threaten their shareholders, the EU commission and the German government to accept a rescue plan, and receive as much as free money as possible without having to give anything (e.g. voting rights, board members, slots).
The threat revolves around the Schutzschirmverfahren (a kind of Chapter 11 bankcruptcy protection scheme in Germany). In order to start a Schutzschirmverfahren Lufthansa must have enough cash in their bank accounts.
That cash is largely sourced from not refunded tickets (where Lufthansa has cancelled the flights for).
Without that cash -> no Schutzschirmverfahren -> no Schutzschirmverfahren means the threat of a Schutzschirmverfahren is gone -> no favourable rescue package with free money!