Wearing a helmet in a car is a PITA. Getting vaccinated causes literally no ongoing inconvenience 24-36 hours later. It's effectively a cost-free intervention with enormous upside in terms of protection from death and hospitalization. Helmets are better compared to interventions like masks and social distancing, as they must be used constantly.

Edit: taking your analogy less literally, it seems the issue here is the socially acceptable level of risk. The health risks of covid are demonstrable and apparent. If we can mitigate those risks by ~90% with no ongoing cost, then that intervention makes sense. On the other hand, if additional interventions mitigate it by only an additional 5%, then those may not be worth the trouble.