I'm guessing it's down to the OEM of the Android phone, not so much the carrier

that's odd. i have had several android phones now, and am always able to turn on talk back right from the start. for reference, I have had galaxy s6, lgg4, htc 10, and now an lgg7

Phones (especially Android phones) come in all shapes, sizes, and qualities, but it is definitely a disappointment to see that some platforms do not have a natively integrated screen reader installed.

>Why isn't there a giant icon of a magnifier on the welcome screen[...]

Because that's bad, counterintuitive UI design. If memory serves me correctly, Apple's launch screen has a small button in the corner that allows accessibility features such as VoiceOver and Zoom to be enabled. Where would a giant icon fit on a screen?

Honestly any phone that doesn't have a screen reader preinstalled should be glossed over by consumers and fined by the government. It's so stupidly easy to put a screen reader, any screen reader, on a phone. Apple's got it covered with Voiceover, most Android smartphones have the Android Accessibility suite preinstalled, and Samsung is off in the corner with Voice Assistant but you can still put Talkback on it. There are so many options that sitting around with one that has no screen reader is unnecessary.

In any case, you're likely preaching to the choir here. Most blind people stick to Apple religiously.

Lol, we should never expect that much from Google.