Because we have the whole world on lockdown waiting for someone to tell us.
Unfortunately, without a vaccine or cure - there are only 2 approaches that work:
1) Eradication - like Taiwan. They have a tiny number of cases in full quarantine. Nobody comes on or off the island without being checked. So they are in total isolation.
But we can't do this.
2) Contact tracing - like Korea. They keep the virus under wraps by aggressively isolating cases, using social policy centered around contact tracing. Of course, they have masks, widespread testing, but a very asserted focus on contact management. FYI we have to get it down to low-levels before this policy can be implemented.
But it works.
Regular 'social distancing' does not do enough. Right now - we are coming out of our 'lockdowns' but the virus will likely just bounce back - why would it not? Other than the fact weather does play a role and it's getting warmer, there's no reason for the COVID growth to come back to where it was.
So either you stay away from other people - or - at least you consent to inform them if somehow you were near them, which requires contact tracing obviously with the addition of good operational capabilities there, it's not 'just an app'.