I think the marshmallow test is pretty flawed itself. But maybe the marshmallow test is actually a good analogy. I suspect many of the test "failures" were caused because the test subject (kid) didn't trust the authority figure (test administrator). When you can see a marshmallow with your own eyes, it's more believable. I think it's quite reasonable to factor in some probability that an untrusted stranger would "alter the deal". If you take the marshmallow now, no one can bait-and-switch you.
And it's starting to look like a pretty good description. There are plenty of people who were on-board with the "temporary" restrictions initially who are now doubting that these promised marshmallows are ever going to be delivered. I'm vaxxed. And I'm done. Good luck on getting your marshmallows.