I took the liberty of checking EDI and LBA and am pleased to confirm that this is not a NCL specific phenomena. The other airports have similar fares. It's also similar on AF to CDG.
I's hazard a guess and the the economy is a fixed ticket and the business class is flexible. As for who buys them, I've no idea. Either that or dissuading people from using biz on the short flights keeping it for those who are connecting long haul and spending thousands with them.
Still for some people checking in on social media 'in the lounge' (cringe) or strutting though the terminal with their business class bag tags proudly on show (double cringe) or strutting up to the gate as the Europe Select/Flying Blue Gold boarding call is made (triple cringe) is a price worth paying for them.