Why does macOS assume PC and PS/2 RTF encodings came from NeXT machines?

According to the RTF specification, \pc and \pca encodings specify the IBM 437 and IBM 850 code pages, respectively.

However, TextEdit and Pages both use the NeXT character set when rendering such files.

https://en.wikipedia.org/wiki/NeXT_character_set

Example RTF code:

    {\rtf1\pc\deff0
    {\fonttbl\f0 Courier New;}
    {\pard
    \'c9\'cd\'cd\'cd\'cd\'bb \line
    \'ba\~\~\~\~\'ba \line
    \'ba\~\~\~\~\'ba \line
    \'c8\'cd\'cd\'cd\'cd\'bc \line
    \par}
    }

This should create a box using curses-like line drawing characters. But on TextEdit and Pages, it does something else entirely using quotes and a superscript number 2.

Does anyone have any historical context?

Did NeXT machines do more word processing than IBM compatible machines at the time?

And why would this deviation from the standard continue today?