NS-10 came out for a different reason. Late '70s was a transitional time in music recording. The divide between the engineer and the artist was blurring and the possibilities for recording engineers to become more creatively involved in the process of producing a record multiplied. This is the time I left Abbey Road as I was not a musician and I realise that I do not have future in a recording studio.
Suddenly these creative recording engineers held the power and some became minor stars in their own right and started to work as freelancers. This happened initially in the US but soon the British studios followed. This new breed recording engineer/producer carried with them a few items of favourite outboard, a few microphones, and a pair of Yamaha NS10s. Yamaha soon got on board and produced a vertical orientated Studio version. It was also less bright removing the need to use a tissue paper in front of the tweeter.
The story I heard at the time is that Bob Clearmountain who was one of the first of those stars wanted a pair of monitors to carry with him so that he had a known reference. He chose NS10 as he wanted something representative of typical domestic hi-fi speakers. (However, this was refuted by engineer Nigel Jopson recently that he was the first to use NS10. Possibly both stories were true as they were apart by an ocean.)
Once Clearmountain and a few other stars began to rely on the NS10, it became a phenomenon and studios began to buy NS10s.
As far as I can recall, it was mostly the newcomers to the exciting world of home recording who wanted to check their mixes in the cars. Didn't help much to the end result.
It was widely known that many 70s mega-stars checked their final mixes on their cars. I know for a fact a few did as I was in their cars having brought the tape with me.
Note: I edited the words I used in the story above so that it doesn't use too similar phrases used in a piece published a while ago as pointed out by
@restorer-john .