The Americans with Disabilities Act became a law in 1990. The people who brainstormed such an act/law wanted fair laws protecting Americans with disabilities.
Title III - Public Accomodations
This title states that people with disabilities may not be discriminated against. When one's website is not accessible to someone who has severe sight problems, for example, then that would be interpreted by some as discriminatory towards people with severe sight problems, because the content-uploader is not being fair towards people with the sight problem.
What One Can Do to Comply with ADA
- One can set headers appropriately, so that the text-to-speech reader can skip and play as the reader wants.
- One can set appropriate colors to be friendly to color-blind people.
- One can make their website easy to navigate with the touch of a single key on a keyboard, for those who have weaker dexterity.
- One can read the full law on this underlined link.