Sunray
Its sunny somewhere.
You're missing the point. It doesn't matter how long it takes them to develop the thing. It takes months or years or infinite time to deploy to devices. On Android it has to go through the OEM like Samsung or whoever. Probably the majority of devices are out of active support. The situation is better on iOS but you only need look at version distribution to see the lag.
It cannot.
I was making reference to future pandemics, once in the OS's of everyone's phones it can be reactivated as a useful tool to help track and trace. I hope I never see another in my lifetime, but I think they are a fact of life until we figure out how to prevent all viruses.