Try to make a puzzle game that has even a tiny resemblance with Tetris and Tetris Company will sue you for copyright violation and force you to remove your game from the market. Make a shameful Puzzle Bobble rip-off? And nothing happens. That's why the market is full of Puzzle Bobble rip-offs, especially at social media and smartphones. Bubble Witch Saga and Angry Birds Stella POP are two famous examples. Then again they 're made from companies which are infamous for making rip-off of other famous games. But now? Even Disney released their own Puzzle Bobble rip-off: play.google.com/store/apps/details?id=com.disney.thoughtbubbles_goo
They aren't good lawyers. The problem is that they go after people who don't have the money/ability to fight it. You can't copyright game mechanics. Hell, you can't patent them anymore either (which recently burned me on a casino game patent I was trying to get through). You can, however, trademark parts of the game or copyright things like names and images. Using any variation of the name "Tetris" is going to be a problem, which is actually what a lot of the games get taken down for.
