Ask HN: Why so many Contact Tracing Apps?

It seems almost every country in the world as well as many states and regions are writing their own contact tracing apps for COVID-19. Research shows that these apps are not useful without significant adoption rates (50% to 80%). I'm trying to understand why so many groups are re-creating the wheel. Why can't they work together and make one really useful app?

https://eclecticlight.co/2020/07/25/smartphone-contact-tracing-has-failed-everywhere/