Whilst asking your bank/CC company to block a merchant is possible, it's not a reliable way of ensuring you aren't charged by the same company again — they could make use of a different payment processor (e.g. going from Stripe to BrainTree) or merchant account, and from the bank's perspective, a different entity made a charge and the ban would not be respected.
That's not to say that asking your bank to block Merchant X isn't useful, but the bank can't guarantee that the merchant won't be able charge you again via a different payment processor/etc., and is why some banks are hesitant to offer this functionality.
That's not to say that asking your bank to block Merchant X isn't useful, but the bank can't guarantee that the merchant won't be able charge you again via a different payment processor/etc., and is why some banks are hesitant to offer this functionality.