That element of an app - proactive, user-driven registration and check-in - makes perfect sense, especially since places like restaurants can (and do) effectively make it part of their process.
If you reduce down an automatic tracing app to a spec of '15 minutes contact', and forget about proximity and whatever, that might also work to a degree. But uptake remains a big problem.
I think my view on this overall subject has shifted slightly not really by anything happening in tech development but, because the real world is such a shitshow, we have gone from thinking about what good looks like to thinking about what 'slightly less bad than now, please, anything' looks like.