RBI mandate is for all banks to be live on BBPS so even small payment apps can process CC bills for it's customers using BBPS API. Indirectly RBI doesn't want monopoly of any one app in this sector.
Now there are 100s of platforms processing CC bills. But BBPS has own limitations.
And IMPS NEFT is old style OG payment system, which cannot be shut off.
BBPS ia just an extra option, while payment apps have to decide that they want BBPS API or build own credit card payment system using IMPS NEFT method.
Hope all doubts cleared now.