Well, most likely it has to do with court cases and risk. Under Rule 11 of the Federal Rules of Civil Procedure, attorneys can be sanctioned for filing frivolous lawsuits. What's more, attorneys like to win, especially when taking cases on a contingency fee basis.
Two big cases have come out recently that suggest a copyright infringement suit can be lucrative even 44+ years after the claim arose. First, the U.S. Supreme Court held laches isn't a bar to these types of suits"
[Writing in favor of the plaintiff who is suing MGM for copyright infringement over the film Raging Bull, Justice Ginsburg] goes on to open a path towards more copyright lawsuits that will undoubtedly be alarming to Hollywood studios.(Emphasis not in original.)
"It is hardly incumbent on copyright owners, however, to challenge each and every actionable infringement," she writes in explaining why a plaintiff might not sue right away. "And there is nothing untoward about waiting to see whether an infringer’s exploitation undercuts the value of the copyrighted work, has no effect on the original work, or even complements it... If the rule were, as MGM urges, 'sue soon, or forever hold your peace,” copyright owners would have to mount a federal case fast to stop seemingly innocuous infringements, lest those infringements eventually grow in magnitude."
Second, the $7.3 million verdict in the Blurred Lines infringement case suggests juries can be persuaded to find infringement where many musicians would not. As we mulled in a previous blog post here, "How can an attorney truly assess the impact of this verdict, and what obligation of sound counsel does this verdict have on a practitioner? In other words, what do you say to a musician who is inspired by or whose works "sound like" a song you already know?"
It seems plaintiff's counsel in the Stairway to Heaven litigation is "you certainly have a case worth pursuing."