The simple fact unless one can point to a legal requirement that the carrier issue a refund, none will be issued.
Even if there is a legal requirement (e.g. in the EU), airlines are still not refunding.
Isn’t the legal requirement obvious enough? The customer bought a ticket for a specific flight route, date, time and fare class - not a time limited voucher without possibility of using it.
There is no such requirement in Malaysia, I guess.
Ultimately, the way the airlines are behaving themselves, will inflict much damage on them. With the Coronavirus pandemic still ongoing, who is in his right mind will book a flight into the future - knowing that the airline may unilaterally cancel the flight and keep the money?