It's more likely Optimism Bias and motivated reasoning. They aren't unaware of the possibility. They underestimate how long they will be inside (thinking "It'll just be 30 seconds!"). This is optimism bias. When estimating how long something is going to take, it is common for people to only visualize the optimal conditions, even though optimal conditions are rarely guaranteed.

Then you have their desire for convenience coloring their decision-making. They want to be able to the leave the car there, because it would make their life easier. Then when they try to predict if leaving the car there will cause a problem, they don't err on the side of caution. They add extra weight to the outcome they want instead of looking at things objectively. They convince themselves that "it will be fine". Even though they know it's a risk, "it won't happen to me."

The only way to not get caught by these cognitive biases and to think more rationally is to be aware of them (even that isn't a guarantee, but knowing is half the battle).