My mom once worked as a gas station attendant and general gopher, back when gas stations had car repair shops attached (late 70s). She used to chain smoke as well. Whenever a customer would complain, she would intentionally spill a tiny bit of gasoline on the ground[1], then put her cigarette out in the puddle. She told me she would never light one while filling, because the spark and flame from the lighter could be enough to start a fire, but that the cigarette itself was not hot enough. I've never repeated this experiment.

1: Yeah I know this is a bad idea itself, but what can you do? She was ~20 and her pre-frontal cortex was still not fully developed.

They just don't burn hot enough to ignite. Remember - things burn at different temps.