It's not a "habit", it's the law. It doesn't matter how the fraudulent charges came to be. If a person disputes a charge and has evidence to show it's fraudulent, then by law the credit card company has to investigate, and deal with it.
It also makes business sense. CC companies make a ton of money with legal transactions, and an anti-consumer, pro-fraud reputation would cost them customers.
> There are numerous reports of identity fraud causing a significant amount of trouble for the consumers involved, and as far as I know, not a one of them has ever received a letter beginning, "We're sorry for the time and trouble you went through to clear this up", with an attached check.
Why would the bank or credit card company send a check? Presumably they're not the one who committed the crime, so why should they cover the damages?
I've had my identity stolen, and it was a PITA to clear up, but the bank and credit companies were reasonable about it, IMO. In a case like this, where it's easy to point at the Equifax breach and say, "See? This is how they got my info.", it's probably even easier to clear up, though I'm sure it's still a hassle.