Manufacturers carry liabilities for the products the make all the time.

That's true for consumer products and even more significant for things like guns.

In most places you're a not even allowed to manufacture guns not to speak of Marketing and selling them.

Offering a service like tornado cash (e.g. getting financial benefits from transaction fees) would be just as illegal if they used potatoes instead of cryptocurrency. There are laws dealing with money laundering specifically and "doing it on the Blockchain" doesn't circumvent them.