A similarly tiny percentage of your users are blind. Another tiny percentage are dyslexic. How many different tiny percentages can you justifiably invite to "go somewhere else"?
Yes there is: the Americans with Disabilities Act. Many private businesses in the States have been - and are currently being - litigated against under said act.
The mandate of the ADA is to provide "full and equal enjoyment" of a public accommodation’s goods, services, facilities, and privileges. Places of public accommodation include, "place[s] of exhibition and entertainment", "places[s] of recreation", and "service establishments". The vast majority of websites are therefore "place[s] of public accommodation", are bound by the requirements of Section 508, and - since roughly this time last year - are required to meet WCAG 2.0 AA (https://www.access-board.gov/guidelines-and-standards/commun...).
In the States businesses are also required to meet the requirements of various human and civil rights laws enacted by states and cities.
And if your company has an international presence, it's also covered under whatever legislation exists in those jurisdictions.
Basically: hell yeah there are requirements to make web content accessible to disabled people. Almost whatever you do, wherever you do it, will be covered to some degree by legislation designed to prevent discrimination.
Of course the existence of financial/technical incentives are good reasons for businesses to make sites accessible, regardless of any legal requirements.
When have you ever know a for-profit business to care if it's not mandated? They only care if it affects the bottom line. As a developer at a company I don't have a ton of say over what we spend time on accessibility-wise and even if I was able to get that code in the QA time to test it would never be approved.
Businesses are not charity. If it doesn't make financial sense to make their website accessible, then they won't unless they're forced to. I'm making no value judgments, this is simply the reality on the ground.
… except that you appear to adjudge a negative financial value to accessibility compliance, when in fact the opposite is true.
Unless that web content is used or maintained by the United States federal government.