(Layman here, take everything with a truckload of salt.)
I'm actually not sure they're "very" different risk profiles, though it isn't unreasonable to assume that before you analyze the situation further. My reason is that contagiousness peaks around 2-3 days before symptoms appear, and the false negative rate for a test is 100% just 4 days before symptoms appear. [1]
Now consider that tests themselves normally take around 3 days to come back. That means if you find out your test results just 1 day before symptoms appear, they'll be based on your viral load from three days prior, where (as mentioned above) the test would've had a ~100% chance of producing a false negative! (Things improve a little for a 2-day turnaround, not that much.) In other news, the only time you can really expect useful results is on (or after) the day of symptoms... at which point you would already be staying home.
I do see 2 places where this argument breaks down:
- For asymptomatic carriers. I don't know what the rates are like, but asymptomatic people won't know to stay home without a test, so tests would seem to have some value there for the purpose of making public gathering safer. However, intuitively, I wouldn't expect it to be a game-changer—I'd only expect it to stretch the runway a little bit (say, get you a few extra days/weeks), but you'd still be back at square 1 having to shut things down afterward.
- For people who aren't cautious and would go out to dine even amidst symptoms, but wouldn't go if they test positive. Which seems ironic because you could say reckless behavior here would (in some sense) seem to create a positive feedback loop justifying more reckless behavior. That not only seems like a questionable way to justify public policy, but it also seems to suffer from the same problem as the last item: it'd only delay the inevitable by a few days/weeks.
- For rapid tests (< 1 day, preferably < 1 hour). I don't expect rapid tests will be available to the masses for everyday activities.
So, at least on my end, with traditional testing that takes 2-3 days to come back, it's entirely plausible (and moreover, likely) to me that testing has low utility for these particular purposes. But I would love to hear an expert's explanation that takes all these factors (and more) into account.
[1] https://medical.mit.edu/covid-19-updates/2020/07/when-should...