I agree with your points about risk budgets not being logically necessary because risks are generally linear and independent. But I think about risk budgets as a supplement to the normal decision-making process, because people aren't good at making one-off decisions in the abstract.
If the party costs 1 hour of expected life, I'll go. If it's 2 hours, would I still go? 3 hours? It's hard to really wrestle with that decision and figure out where the tradeoffs aren't worth it. "1 hour" is already a more concrete framing than "2 micromorts", but you're still trading off a concrete outcome (going to a party) with something pretty abstract (1 hour expected value of life), so it's hard to make logically consistent decisions that don't vary with your mood, etc.
If, instead, you set an overall weekly risk budget, you can then trade off between specific concrete choices. "If I go to this party, I can't go to the grocery store. Which would I rather do?"
So it helps to make yourself more consistent and make your decisions more concrete. Help you "set policies" (and be consistent with them) vs. "making initial decisions" to gjm's point in the other comment.
Would be interested in your thoughts!
To the point on test positivity rate remaining stable: non-COVID respiratory disease incidence is up significant (common cold, etc) - because they are no longer suppressed by behavior. There is a NYT article today with more information: https://www.nytimes.com/2021/07/22/well/live/colds-summer-immunity.html?action=click&module=Top Stories&pgtype=Homepage
It is possible that many people have non-COVID colds/coughs and are getting repeatedly tested, and that is offsetting the expected increases to the positivity rate.
On the topic of Jen Psaki, this was pretty spot-on:
The Onion: "‘And What Do You Want Me To Do, Brush Every Night?’ Snaps Jen Psaki At Dentist Suggesting She Could Improve Oral Hygiene"