Light text on a dark background can be illegible for people with astigmatism. (Somewhat depending on the axis of astigmatism vs. the direction of text.) Or if not illegible, at least a blurry, uncomfortable mess to read.

Astigmatism is very common, and not all astigmatism is corrected or correctable with glasses or contacts. Contacts, especially, are hit-and-miss for correcting astigmatism. Toric contacts, which are weighted to rotate into (hopefully) the correct position over the eye, are sometimes too uncomfortable or too unreliable (because they rotate out of position) compared to non-toric lenses. And besides, many people use their computer or phone without their glasses on/contacts in.

Additionally, dry eyes or other eye conditions can sometimes cause similar blurring issues with light text on dark backgrounds.

So, I ask that people please do include light mode options for accessibility. Even a half-assed implementation of light mode is better than none.

(If you insist on only supporting dark mode, low-contrast dark modes tend to be a bit better for astigmatism than AMOLED/true black dark modes. I suspect this might create problems for people who need high contrast in order to make out the text, however. I haven't looked into how well high contrast system modes function these days.)

I always switch to a light theme when the sun is shining on my screen

Accessibility plays a reason other than just taste.

Eh, I personally like the light theme better. But if others would decide that I too shall ever only perceive bright text on dark background, I guess I could live with that as well.