Lord of the Rings had been published in the 1950s, but it got big when Ballantine books published it in paperback in the US (after Ace books had published an unauthorized version, as recounted in a thread I started a couple of months ago. Some have attributed LotR’s ultimate publicity to that initial event). I first heard of it in the late 1960s, by which time it was already a hit on college campuses. Heck, the parody, Bored of the Rings came out in 1969.
But with LotR popular, they began scrambling for other fantasies. There had been a fantasy paperback market before this, but this breathed new life in as Ballantine published E.R.R.Eddison’s ungodly long books (The Worm Ouroborous and others), Mervyn Peake’s Gormenghast trilogy, and Lin Carter started scouring for “Adult Fantasy”, collecting the works of Clark Ashton Smith and others.
Ace had published LotR, as noted, and now republished Silverlock. Lancer had already been publishing Robert E. Howard’s Conan books, and his other works, and now stepped that up. The comics, quick to spot a trend, took it up. Marvel brought out Conan the Barbarian comics, followed by King Kull, Howard’s other hero. DC retaliated by buying the rights to Tarzan and then also publishing Edgar Rice Burroughs’ other series – Carson of Venus, Pellucidar, and John Carter of Mars. Marvel retaliated by publishing Gullivar of Mars, based on the book by Arnold that some claim Burroughs cribbed John Carter from. DC put out Sword and Sorcery, featuring Fritz Leiber’s Fahferd and the Grey Mouser. Sadly, it only lasted six issues (Marvel arguably retaliated by introducing the characters Fafnir and Blackrat into the Conan stories. They quickly got killed off.)
This was all before 1973, so it predates most of the stuff in the OP, but it shows that there was a fertile interest in Sword and Sorcery in novels, magazines, and comics from which games and rock music could draw. (Even before Thomas Covenant, by the way, Terry Brooks had come out with The Sword of Shannara, which was practically plagiarism, but it spawned a whole series. )