This probably had more to do with the practical fact that ink is black

We can and do make ink of any color. Black is just the most popular. And we could make paper of any color.

But it's probably true that printing white ink on black paper is harder.

Then again, if that was the best way to read, we should see some, if expensive such books.

The problem is that black paper would still have some reflectance depending on the surrounding lighting, potentially rather higher than reflectance of black ink.

Traditional off-white paper lit by ambient illumination is not the same as an active emitter of light with a color temperature well higher than ambient. FWIW modern paper is actually brighter than white (it fluoresces).