Answer:
Because testing and research done on human beings has been not accepted either by the scientific community, or society at large, the only other tool that could be used in order to answer questions as to how to make human life easier, was through animal research. As such, science chooses animals that are genetically similar to human beings, in order to test their theories, and thus generate results that become either products, or services, that improve human life.
Such is the case of medicine, and pharmacology. Although pharmacology´s origin is from plants, many of these chemicals could not be tested on human beings because of ethical, and humanitarian issues, and therefore, the only other, and best option, was to use animals. Thus, many laboratories have developed many of the substances that today save human lives thanks to these animals that were used in research.
An example like this was the development of insulin. An enzyme produced by the human body normally, but that in pathological situations, may be either faulty, or absent totally, is now produced thanks to research on animals whose insulin, and bodies, are used for both extraction and also testing.
Like this, many other such advances have been made in the medical field and have benefited families, and friends.