HDFC and other banks are banning cryptocurrency purchases through debit and credit cards

So Just received a mail from HDFC Bank which says that HDFC Credit/Debit/Prepaid cards cannot be used to trade/buy cryptocurrencies.

And looks like Citibank and Kotak Mahindra Bank did the same last month. Any more Banks which have done the same?

Seems this decision has to do more with business and reward points than anything else. HDFC still allows transferring funds using net banking (Correct me if iam right on this)
Then why this selective blockage only for credit and debit cards? Maybe they don't want to get reward points to such transactions...
I dont think the Govt has banned crypto transactions. Why are some banks getting hyper active on this?