Even if that were true, individual bargaining power is irrelevant here as the workers share a collective agreement that clearly asserts that Amazon will not terminate employment for reasons related to safety.

Logically, the workers knew there was no onus for them to leave their cars. But when your friendly coworker comes along "I know it is warm in there, but can you please come outside with the rest of us who don't have the same luxury?" it is hard in Canadian culture to say no. Rather you get "Sorry. I'll be right there."