This has no basis in reality. Putting a feature like this upfront will cause more accidents than it will allow people with vision issues to use it frequently. People with vision issues need almost all text to be larger. These same people will be the ones accidently hitting this bar instead of brightness and not knowing how to fix it.
I have very bad vision and I use the feature regularly but I imagine I‘m like 1 of 500 people. Accidents are not an issue though since I oversold it being as easy as brightness. You need to force press the icon before you can slide up/down.
I‘m really not sure what else Apple could do other than:
- Asking during onboarding
- Putting it in Display as well as Accessibility settings
- Having a control center button