There are numerous safety and data privacy issues with contact-tracing apps. For example, Iran developed an app called AC19 which was swiftly banned by Google. This is because they were planning on collecting much more data regarding individuals than Google's laws and mandates allowed.
Also, in China, systems were introduced that could easily collect an individual's payment history, identity, and location once the app was installed. Local police could even be notified of these individuals and action could be taken against them. These are just some of the privacy risks involved with such an app. In order to truly trace the spread of the virus, governments would have to tap into personal history and data. To add to this, these apps have not been proven to make a dent in countries that are already using them. Is it worthwhile or even reasonable to pay such a high price for an idea that may or may not work?