Just maybe, the Estate thinks it just isn't worth trying to sort out the innocent uses of copyrighted material from the less-than savory.
It goes beyond that; it is in fact an imperative created by the nature of trademrk law. You see, a trademark has to be enforced if you want to keep it- if you don't assert ownership continually then the argument can be made, successfully, that the trademark has passed into the public domain as happened to, for two examples, Nylon and Aspirin. Xerox' lawyers were notorious for hurling C&Ds at any and everyone who used "Xerox" as a synonymn for "photocopy," and pretty much succeeded in suppressing it- and it was for that reason. All that's necessary to make such a case is that the trademark-holder has known or even should have known about unauthorized use, and done nothing about it.
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Hammond and Scull's frankly creepy literary stalking job I leave in the gutter
