I mean, it's my computer. I should ultimately be in control of how a document renders. I might need larger text due to poor eyesight, or need to use a screen reader. Or I might just be irritated that the web developer just up and decided that light gray on dark gray text looked cool (it doesn't, it barely can be read). Or I might want to scroll with my keyboard because a mouse is painful to my RSI. If I go out of the way and set up accessibility settings, I would expect all applications on my device (including the web browser) to respect those settings.