It would help to know what exactly you mean with "easier to read". That's only a vague description.
Some screens seem more aggressive than others, so that users have to turn down the brightness a lot, or they have to use "dark modes" to reduce their symptoms. Why? No really knows. I suspect it's related to the spectrum. Especially White LEDs seem to cause this issue. But there are exceptions. Again, no one really knows why, but it could be slight differences in the phosphor that covers the LEDs. This theory doesn't fully make sense if you think about sunlight having the full spectrum of all wavelengths in a much higher intensity and not causing such issues. There's a clear lack of research here. No doctor could ever explain to me why sunlight is OK but a much darker White LED screen/bulb is not.
But it is as it is, and another thing I noticed is that on very usable screens, the few that there are, I prefer white backgrounds. Perhaps it is the same for you, and you feel the need to reduce the white's intensity on your aggressive screen. Ultimately leading to preferring white on black.