not illegal to alter or base something off of a design, but it sure is to just print a copy of the original design onto something and slap it on a card like most of these are
this isn’t always true at all, and isn’t the problem in this case. This is more a case of counterfeiting when a card is just trying to copy the original, than profiting off IP. If I draw a pikachu and slap it on a tshirt I can sell it all I want as long as I don’t call it an official design. This is just one example of thousands and thousands.
the US, contrary to some people’s belief has extremely lax copyright and IP laws compared to almost anywhere else on the planet besides China
I wouldn’t argue anyway, this was one of my major areas of study when I was in college. It would be exceedingly difficult for tPCI to do just about anything to these individual sellers, it wouldn’t be worth the cost to show up at court, and even then Free Speech parody and transformative allowances always has a soft spot in people’s hearts during individual rulings. the only time a company would even dream of it is if there was big money involved.
it goes the other direction too. Most people don’t know the online ccg Hex, but having worked on the game I can tell you they were sued by Wizard’s of the Coast as infringing on Magic. There wasn’t a good basis for it, but Wizard’s kept Cryptozoic in court for almost 2 years with different reasons over and over until they finally decided to just settle the matter monetarily.