Word quickly spread throughout the lands of a magical new and beautiful guitar and bass born from fire that could threaten the Fender stranglehold. The mighty Fender ogre Ceebee Ess instructed his finest lawyers to craft a lie about the Firebird and claim it was stolen from the land of Fender. Gibson being very afraid of Fender redesigned its guitar but in a swipe of defiance they claimed the new design to be not backwards like Fender guitars, and the new Gibson was called the Non Reverse.
Seeing that Fenders best attempts to destroy the success of the Fire and Thunderbirds had failed, the mighty ogre summoned his witches warlocks and spell binders to conjure up a curse that would instead confound guitar and bass players and cause a great vail to cover their eyes and ears so that they would not see or hear the truth but instead constantly repeat rumors and untruths every time a Firebird or Thunderbird is mentioned.

Fun interpretation...
but.., frankly Gibson and Fender, along with Gretsch, Guild, Rickenbacker et al were all just selling guitars/basses. Gibson guitars where actually more similar to Guild, Gretsch, and Rickenbacker guitars. Leo Fender introduced something different (solid body/detachable neck) and they all followed (eventually). Fender had no fear of Gibson basses (or any other brand for that matter) because most pro's favored a Fender bass and it defined '50s-'60s music. So that was one of a few reasons the 'lawsuit myth' didn't make sense.
Gibson's bean-counters reading the bottom-line lead to discontinuing the R and to create the NR, and ended production of both for about 5 years. It was simply that not enough of them were being sold. Nothing romantic about that.