Diaper changing tables are a modern convenience that makes changing a baby's diaper easier and safer for parents. Several retail stores and restaurants provide diaper changing tables in their public bathrooms. While these diaper changing tables are not on par with the home models, they are at a comfortable height for parents to change their children’s diapers.
Federal laws do not require changing tables in bathrooms. Stores are not required to have changing tables. The stores that provide them are only offering a convenience for their customers. Where changing tables do exist, they only accommodate children under 40 lbs.
Public bathrooms are not the responsibility, but a courtesy of stores to their customers. If it does not suit your needs, there is at least a bathroom. This is not akin to having handicap accessible bathrooms. While it is a bother to parents, it is not a hindrance to equal access. Not having changing tables in public bathrooms is not discrimination. There is no intent to exclude parents and their babies.
There is no obligation for stores to supply changing tables since there is no law requiring stores to provide bathrooms. Changing tables are only available for customer convenience. They can be thought of on par with or similar to valet parking, on-site tailoring, and free samples. Stores will attract more customers if the store offers certain amenities, which is the idea behind offering changing tables.