The inverse (Windows deliberately not looking like Mac) seems likely to have been at least partially responsible. Apple were litigious about their design language - with the ‘trash can’ being a particular point of contention. Microsoft were probably at least a little cautious about looking too Mac-like. Indeed Apple in the end did sue MS for stealing ’look and feel’ elements in 1988 (literally the context in which the term look-and-feel was popularized), ultimately unsuccessfully - except for the trash can being recognized as distinctive enough to not be allowed to be copied, leading to Windows’ 90s classic ‘recycle bin’.

You can invert the cursor color on windows fwiw

You can change the colors (the default is black with a white outline, not just black) on Mac, too.

I used to find it irritating that I had to jiggle the mouse to find the cursor, because it doesn't really stick out on screen when it is white or black and I have a lot of screen area. Then I tried turning the cursor yellow with a black border. It is great, it's obvious where it is with a glance now.

Intrigued by your comment, I've just tried it. Man, it's really working. It's really effective, I'll try to adapt to the colours and see if I keep it!

Windows 1.0, with a white cursor, was released in November 1985.

Mac OS 1.0, with a black cursor, was released in January 1984. Its predecessor, Lisa OS, with a black cursor, was January 1983.

So if anything, maybe Windows cursor was white just to be different from Mac.

But also, according to Wikipedia, Windows 1.0 was inspired by Visi On [1], which also used a white cursor (pointing upwards, rather than up-left) [2]. So it might have just copied that?

But just from a logical standpoint, Mac always used a white document area with black text in windows, where it would make sense to have a black cursor easy to see. While Visi On continued the MS-DOS/terminal tradition of white text on a black background in its windows, where a white cursor would be more visible. But a quick Google search though doesn't seem to produce any authoritative answer for why Windows 1.0, with its white backgrounds, would choose a white cursor. All I can find is [3] but it's paywalled and none of the usual cache/archive services can access it.

[1] https://en.wikipedia.org/wiki/Windows_1.0x

[2] https://en.wikipedia.org/wiki/Visi_On

[3] https://www.quora.com/Why-is-the-default-mouse-cursor-black-...