... except ... when I write iOS software (for the most successful product of all time), I am frequently using types that have "NS" prefixes.
I wonder where they came from?
A decade or so later, Apple was on the tail end of a long, slow, downward slide. The team wasn't happy with the current state of their Mac operating system, and bought out NeXT to use their software as the basis of its replacement (Mac OS X).
Jobs, as CEO of NeXT, came back to Apple as a consultant, but was CEO again in a matter of years.
No, Apple bought NeXT after the failure of Copland to birth a replacement for the creaky and leaky MacOS (BeOS was the big alternative, but Apple thought they were asking for too much).
And NeXT proceeded to take over: Apple bought NeXT in February 1997 keeping Jobs back as an advisor, Jobs staged a boardroom coup to remove Amelio in July, and was then named interim CEO.
Following that he started cutting into the existing product lines and placing NeXT people (Tevanian , Forstall), promoting people he was interested in (Ive), or hiring them from outside (Cook). Basically reshaping the company.
Your definition of success seems extraordinarily high, if these products were failures. Maybe measured by items sold. But then each of them stands in nearly every single design museum like MoMA, history books, and were clear stepping stones to the Mac mini (cube, sunflower without display), and ipod/phone (newton). So bottom line they were a clear success to Apple’s enormous brand value.