It's not only their god-given right, in many cases, it's their statutory duty. If you don't protect your trademarks, you lose them. Trademark goes beyond names and words, and includes things like packaging and, arguably, a board game's layout and distinct board coloring. Hasbro owns trademarks on Clue and Scrabble. If they wish to maintain those trademarks, they need to sue to protect them.
Should Hasbro commit fiscal suicide by letting random people copy their IP and ideas? There's a reason why our legal system protects creative works and provides creators with protection. You may think that the system is corrupt or broken, but how else is Hasbro supposed to stop me from copying Scrabble and releasing my new board game "Spell-o-grid?" Sure, their version may be made with a higher quality board, and maybe they only use the standard 26 "english letters," but mine is substantially cheaper, and if you flip over the qy and qj tiles, you can use them like Hasbro's "blank" tiles.
Or is it your position that it's okay for people to copy Hasbro's products, but not a small company or individual designer's work?
Hasbro does what it can because Hasbro must protect those rights.
--G