It's similar for all "large banks", after repo rate cut, everyone is cutting off their rates. I don't know of any large bank giving 8%+ interest today.
Also, the discussion on this thread is not regarding free credit card. It's basically around wealth / HNI accounts.
Also, you are forgetting that parents and senior citizens tend to keep their money in FDs and are very light on equity. So primary account can be made of them while secondary users get to enjoy all benefits as well. It's not a straight calculation like you're suggesting.
I'm sure there are many self employed people like me who move their day end balance from current account to savings account and transfer it back the next morning. Gives you the needed MAB, gives you free savings interest which you otherwise wouldn't get on a current account, doesn't cost anything to move balances. So maintaining MAB is seriously not an issue.