Trademarks are supposed to designate the source of a product or good--not the good itself--and you have to actually use it in practice. The estate could have probably created Sherlock brand corncob pipes and maintained a trademark. But that wouldn't allow them to block someone from making a Sherlock Holmes movie or reprinting the books.

It might work for Disney because they have real products and can use Mickey to brand them. Even that won't stop someone from making Steamboat Willy 2. But it might block someone from making MickeyLand Amusement park.