Apparently, the Tetris Company is a copyright troll / vexatious litigant.
According to Tetris Holdings LLC v Xio Interactive, the 10x20 play area and block shapes are somehow copyrighted, despite these being declared public domain previously.
Therefore all Tetris clones are somehow illegal. Absolutely insane.
Ashtear@piefed.social 1 hour ago
The answer to both is variations on public domain works can be protected by trademark and copyright. Type A isn’t Korobeiniki, it’s a new work. It’s the same reason why Disney’s Snow White is protected by copyright (for a little while longer, anyway), but the original work it is based on is not.
You want this kind of protection. Otherwise works would effectively be held by the original artists in perpetuity, as a lack of protection even after they enter the public domain chills any investment in variation on those works that might lead to significant cultural impact.
I encourage you to read up on the basics and the reasons why these laws exist in the first place. This sort of thing is how we end up with misinformation like “piracy is legal if you own the original game” and “it’s 100% legal to jailbreak a video game console.”