Wearing a helmet on an airplane isn’t a perfect solution to airplanes crashing but it could potentially save your life, but we seem fine with the risk trade off of not wearing one. No decisions we make about responding to COVID will be risk free, the question is which trade offs we should accept. No matter how much pressure is put on the unvaccinated some people will refuse to get it, and unless you’re suggesting administering it by force eventually that tactic will meet diminishing returns.
You picked the wrong example. Helmets will do very little to reduce fatalities from air travel simply because the mechanics of how those fatalities occure.
Wearing a helmet while driving a car, however, has a pretty good chance of reduxing injuries and fatalities (probably even better than wearing a helmet when riding a bike on a seperated bike path.)
I don't think this is really a question of people analyzing the trade-offs. This how to do with how the risks and the activity are percieved, people are generally really at accurately assessing such risks.