Here’s the thing– hair burns really fast.
There’s a puff of smoke, and it shrivels away and is gone. Even with the patchy nature of Junkrat’s hair (clearly some has been lost along the way) he just can’t sustain this level of smouldering.
A proposition– Junkrat threads fuses into his hair, and lights them on fire before battle. This works to confuse and intimidate the enemy for those few moments before he blows them sky-high. You just don’t expect to see a man with his head on fire. It’s also convenient for him to have a source of flame in case he needs to light something up in the middle of a fight.
I imagine he’d be pretty proud of his innovation. When Roadhog sees him weaving fuses into his hair and goes “oh, like Blackbeard” he would be livid. Demanding to know what drongo was stealing his style. “Where is he? I’m going to blow him up and dance on his corpse!”
It takes a while for Roadhog to calm him down enough to explain that Blackbeard died a very long time ago.
Still, a surefire way to piss Junkrat off is to mention Blackbeard. Lit fuses is Junkrat’s style. Doesn’t matter if some crusty old pirate thought of it back in ancient times.