George Romero literally invented the modern zombie. NotLD was massively successful on its own, and spawned a genre of horror literature that to this day is a dominant trend. It was a brilliant piece in a college-level production. It was a lot like Clerks, but even more so.
NotLD became public domain when they changed the name of the film from Night of the Flesh Eaters to Night of the Living Dead. While the change was obviously brilliant, the distributor didn’t include the copyright notice in the updated prints that were sent to the theater. That one mistake by someone else cost Romero untold tens to hundreds of millions of dollars.
I think we are all in favor of work being published in the public domain. As a scientist, I paid thousands of dollars per paper for everything I published to make sure they weren’t locked behind a $30 paywall. I’ve been a vocal supporter of FOSS since my first slackware install in the mid-1990s, and even before that with the cypherpunk community on usenet.
But NotLD is a counterexample of the goodness of non-copyrighted and non-patented works. It was not only done without the permission of the creator - which is key to the ethos - it is taken advantage of by every third rate company who sells a copy of it for $1.99.