It didn't have to though.

Lotus 1-2-3 mimicked a spreadsheet and it is not searing white.

Windows 2 was predominantly dark text on white background. Same with GEM on the Atari ST. Both current in the late 1980s.

Sinclair's ZX Spectrum was black text on white background in 1982.

There's no 'likely' about it - the Mac absolutely used white as its background color for document windows and finder folders. It was striking and different when you first encountered one of the early compact Macs to see how white the screen was when you opened MacWrite.

As for the claim that Macs had no 'mainstream use' for 20 years until the Intel switch... your personal Mac-free life is a sad story, but not remotely universal, and while it's certainly true that Macs always had minority market share, it's insane to suggest they weren't influential.

My favorites were actually DOS TUIs, where for some reason blue became a commonly used background color for a lot of things (e.g. Norton Commander, many Borland products, FoxPro...).

Amigas used blue and Atari GEM, alongside DR-DOS and MS-DOS Doshell used white.