What is the basis by which you are claiming ADA compliance implies their drivers are employees? Providing usable service for ADA customers can and should be accomplished regardless of Uber/Lyft's driver contracting model.
Employee classification is dependent on the amount of control that a company has over the worker. Uber has consistently argued that they have minimal influence over driver behavior, in attempts to keep their status quo on their workers' current classification, and avoid the costs associated with having employees.
The more 'hands-off' that Uber can assert that they are with their drivers, the better for their argument. They want to be 100% a middleman and 0% anything else. Ultimately, I think they'll fail, but for now, that's their strategy.