That just prevented CRT degradation and it had less ghosting and flickering, especially as most CRTs in the home computer era were just terrible home TVs, and CRTs in the mainframe era were equally terrible. The saturated blue background was absolutely insufferable and I had ghosting and shifted color perception for minutes after using NC and Borland software for a long time. I loathe it till this day, just like garish CGA colors which were an assault on my eyes.
80's and 90's had a general concept of a desktop with windows as paper documents, because the first real use case for personal computers and workstations was assisting office jobs.
Funny how you call the normal light scheme inverted. IIRC PC text/graphics modes used this term for dark backgrounds.