[hvac]

This is precisely correct, especially wrt the cost/benefit. The antibody tests won't tell you when you were infected, with which variant, or how much viral dose, on top of their imperfect accuracy. And if you're going to bother going to a hospital to get your blood drawn, why not just... get the shot and remove all doubt?

Does the calculus change in the countries where vaccines are basically nonexistant? Yes, of course. But vaccines in the US are as nearly easy to get as Gatorade now, and have been for several months. We spent many billions making it that way - we don't need to turn around and start spending even more money on pox party incentives.