At least partly because they're not allowed to do that because there are specific rules about it. If banks could just say "so sad, too bad", they absolutely would. I know someone who had to resort to the financial ombudsman to get their money after a hack because the "bank" (Revolut or Monzo) would not engage with them to even acknowledge anything had happened.

Pretty much this is what banks try if they can: https://youtube.com/watch?v=CS9ptA3Ya9E