Earlier quoted context omitted.
Why? The initial setup is for the things you set once and never need to change. I tell my phone I want it in English during on boarding - and then I never need that setting again.
Eyesight changes over time. People learn new languages, and want to switch. Making these decisions for the user and then forcing them forever is decidedly un-user-friendly.
It's not like you're learning a new language everyday. Nor losing your eyesight. Keep in mind that the life of a cellphone is anywhere between one and six years, for most tends to be around three (speculation). Isn't reason enough to make it a top priority for people to be able to access language / text size changes in their settings everyday.