There's no particular incentive for the changes made after the sale to improve functionality, particularly if the nominal owner of the machine can't detect them. If your wash efficiency is better this month than last month, wouldn't you like to know what change caused that? How about if it's worse? What if it accidentally breaks your dishwasher? Or the new, more efficient settings no longer get your dishes fully clean?

I don't think there's a terribly strong incentive for Miele to actively break their customers' deployed machines, since those customers might buy a Bosch next time, but there isn't a terribly strong incentive for them to improve them either.

There is a strong incentive for Miele to find ways to sell their customers' personal information, for example to insurance companies, collection agencies, or police forces, and this is functionality that can be added later in a firmware update.

Better to leave update functionality under the control of the people who are most directly affected by it: the users.