There are at least two major types of disadvantages that can happen in such a situation.
First, there is the danger of government sanctions. Lawsuits can be filed against your firm if it does not comply with this act. These things can lead to financial losses for your firm.
Second, there are losses that you can incur by making it difficult for disabled people to work and/or shop in your establishment. A store that makes it difficult for disabled people to enter, for example, loses their business. Similarly, a firm that makes it hard for disabled employees to work loses out on their potential talents. This sort of loss of business or of talent is another disadvantage incurred when a firm does not obey this law.