*Two key groups had opposed the 1990 ADA*
Opposition From Religious Groups
Debate over the Americans with Disabilities Act led some religious groups to take opposite positions.[ Some religious groups, such as the Association of Christian Schools International, opposed the ADA in its original form. ACSI opposed the Act primarily because the ADA labeled religious institutions “public accommodations,” and thus would have required churches to make costly structural changes to ensure access for all. The cost argument advanced by ACSI and others prevailed in keeping religious institutions from being labeled as “public accommodations,” and thus churches were permitted to remain inaccessible if they choose. In addition to opposing the ADA on grounds of cost, church groups like the National Association of Evangelicals testified against the ADA’s Title I (employment) provisions on grounds of religious liberty. The NAE felt that the regulation of the internal employment of churches was "... an improper intrusion [of] the federal government."
Opposition From Business Interests
Many members of the business community opposed the passage of the Americans with Disabilities Act. Testifying before Congress, Greyhound Bus Lines stated that the Act had the potential to “deprive millions of people of affordable intercity public transportation and thousands of rural communities of their only link to the outside world.” The US Chamber of Commerce argued that the costs of the ADA would be “enormous” and have “a disastrous impact on many small businesses struggling to survive”.The National Federation of Independent Businesses, an organization that lobbies for small businesses, called the ADA “a disaster for small business.” Pro-business conservative commentators joined in opposition, writing that the Americans with Disabilities Act was “an expensive headache to millions” that would not necessarily improve the lives of people with disabilities.
It's interesting that the original ADA was signed into law by a conservative Republican. George HW Bush had courted the votes of both the business community and 'social conservatives' (conservative Christians). Ditto for his son who signed the ADA Amendments Act into law.
I believe that this helped blunt the opposition and enabled the law to be passed.